Chapter V: Part 5

FIG. 30.—Encysted cystic stage of _H. diminuta_: _caud._, caudal
appendage; _cyst._, adventitious capsule inclosing the cercocystis.
Enlarged. (After Grassi & Rovelli, 1892a, pl. 4, fig. 1.)
]

From present evidence, the rats and mice are looked upon as the regular hosts for this worm, and hence as the natural reservoir of the infection. The intermediate host becomes infected from the rodents and then transmits the infection to man.

It might be mentioned that as yet no extensive study has been conducted in the United States to differentiate clearly the various species of _Hymenolepis_ found in our rats and mice. The possibility is therefore not entirely excluded that some of our cases of _Hymenolepis diminuta_ may eventually be shown to be referable to other species of the same genus.

NEMATODA—TRUE ROUND WORMS.

Family TRICHINELLIDÆ.[AA]

Footnote AA:

SYNONYM.—_Trichotrachelidæ._ It becomes necessary under the
international code to change the family name; the family name
_Trichinellidæ_ is chosen as less likely to lead to confusion than a
family name based upon _Trichuris_.

FAMILY DIAGNOSIS.—_Nematoda_: Elongate cylindrical worms; cephalic
portion long and very slender, caudal portion more or less swollen.
Mouth rounded, without lips. Esophagus relatively very long, composed
of a single row of large cells, forming the so-called “cell body” and
supporting a narrow esophageal tube; anus terminal or nearly so.

Male: With a single spicule or without spicule.

Female: With one ovary; vulva near caudal end of cell body, close to
point where body increases in diameter; oviparous or viviparous.

Eggs: Oviparous species, with thick shell, with opening at each pole,
closed by a transparent plug.

TYPE GENUS.—_Trichinella_ Railliet, 1895.

This family furnishes two parasites to man: The whipworm (_Trichuris trichiura_) of the colon, and the trichina or flesh worm (_Trichinella spiralis_, see p. 101).

Genus TRICHINELLA[AB] Railliet, 1895.

Footnote AB:

SYNONYMS.—_Trichina_ Owen, 1835 [not Meig., 1830, insect.];
_Trichinus_ Fraser, 1881a, for _Trichina_.

GENERIC DIAGNOSIS.—_Trichinellidæ_: Very minute worms, of nearly
uniform diameter. Adults in intestine of mammals, larvæ encysted in
muscles.

Male: Without spicules, but with 2 conical appendages on the tail, at
side of terminal cloacal opening.

Female: Vulva about one-fifth the length from anterior end;
viviparous.

TYPE SPECIES.—_Trichinella spiralis_ (Owen, 1835) Railliet, 1895.

TRICHINELLA SPIRALIS (Owen, 1835) Railliet, 1895.

[Figs. 31 to 51.]

SPECIFIC DIAGNOSIS.—_Trichinella_: Body thread-like, visible to naked
eye.

Male: Length, 1.4 to 1.6 millimeters; diameter, 40μ; distal of cloacal
opening, 2 pairs of papillæ, the anterior pair hemispherical,
posterior pair conical.

Female: Length, 3 to 4 millimeters; diameter, 60μ; anus terminal;
vulva one-fifth of length of body from the mouth; viviparous.

HABITAT.—Adults in lumen and wall of small intestine, encysted larvæ
in muscles of various mammals, particularly in rats, mice, swine, and
man.

GEOGRAPHIC DISTRIBUTION.—More or less cosmopolitan.

SOURCE OF INFECTION.—From the life cycle of this parasite it is clear that the permanent reservoir of infection must be some animal with cannibalistic tendencies. Of the three most important hosts (man, swine, and rats), the rats present ideal conditions in this respect. It is true that there are some tribes of man which are cannibalistic, but their distribution is restricted. Likewise swine are in so far cannibalistic that they eat uncooked swine offal and swill, but this is due to the shortsightedness of man rather than to the habits of the swine. Accordingly, neither man nor the hog presents the proper theoretical conditions for the perpetuation of the parasites and hence to serve as reservoir for the disease it causes.

Rats, on the contrary, are cannibalistic, and trichinosis is a common disease among them. Hence they may be viewed as the natural reservoir for the parasites and for the disease it causes; hence, also, any well-directed public health campaign against trichinosis should consider the eradication of rats.

Rats become infected by eating each other; by eating scraps of pork found on the offal pile of slaughterhouses, or in swill; and by eating scraps of human flesh in dissecting rooms of medical schools.

FIG. 31.—Female trichina from the intestine; 24 hours after infection.
Enlarged. (After Leuckart, 1866a, pl. 1, fig. 1.)
]

Swine become infected by eating rats, and by eating scraps of pork on the offal pile of slaughterhouses, or in swill.

Man becomes infected almost exclusively by eating pork and boar meat. The rare infections which occur from eating other meat are almost negligible.

MEDICAL SIGNIFICANCE.—_Trichiniasis_ or _trichinosis_ refers to infection with the trichina or flesh worm. Normally it occurs only in mammals, chiefly carnivorous and omnivorous species, and it is transmissible from any infected mammal to any other mammal susceptible to it, in case the latter eats the uncooked flesh of the former.

_Symptoms._—In heavy infections there may be three more or less distinct periods of the disease, corresponding to the three stages in the life cycle of the parasite; but these stages are obscure in light or in repeated infections. Profuse sweating may last during the entire attack.

FIG. 32.—Gravid adult female trichina. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 2.)

FIG. 33.—Adult male trichina from the intestine. Enlarged. (After
Leuckart, 1866a, pl. 1, fig. 5.)

FIG. 34.—External genitalia of same. Enlarged. (After Leuckart, 1866a,
pl. 1, fig. 7.)

FIG. 35.—The same with extruded cloaca. Enlarged. (After Leuckart,
1866a, pl. 1, fig. 8.)

FIG. 36.—Cephalic portion of a trichina showing central nervous system
and anterior portion of intestinal canal. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 13.)

FIG. 37.—Transverse section of a female trichina. Greatly enlarged.
(After Leuckart, 1866a, pl. 1, fig. 16.)

FIG. 38.—Young trichina embryo in a muscle fibre. Greatly enlarged.
(After Leuckart, 1866a, pl. 2, fig. 1.)
]

Period of ingression: The adult parasites are in the intestine, hence gastro-intestinal symptoms develop; irregular appetite, nausea, diarrhea or constipation, colicky pains; a temporary edema around eyes about the eighth day; muscular pains begin.

Period of digression: This begins about the eighth to the fifteenth day, sometimes later; young embryos are wandering to and attacking the muscles, hence muscular symptoms (myositis) develop; painful tension of muscles, especially biceps; members assume semiflexed position; movements, chewing, swallowing, breathing, and speech become difficult; eyes become fixed; fever.

FIGS. 39–42.—Later stages of same; the muscular structure is
undergoing changes. (After Leuckart, 1866a, pl. 2, figs. 3, 6, 7,
8.)

FIGS. 43–45.—Muscle trichinæ, 0.3 mm., 0.4 mm., and 0.6 mm. long.
(After Leuckart, 1866a, pl. 2, figs. 10–12.)
]

Period of regression: The parasites become encysted in muscles. All symptoms may increase, then gradually decrease; cachexia and anemia resulting from malnutrition; pruritis, miliary cutaneous eruptions; desquamation; about twenty-fourth day, a “second” edema develops, especially about the face; lungs may become edematous; bronchial catarrh, pneumonia, or pleurisy may appear; gradual recovery.

FIG. 46.—A female trichina from the muscle. Greatly enlarged. (After
Leuckart, 1866a, pl. 1, fig. 12.)
]

FIG. 47.—A piece of pork with encysted trichinæ. Enlarged. (After
Braun, 1903, p. 251, fig. 195.)
]

_Lethality._—The lethality varies from 0 to 100 per cent; it averaged 5.6 per cent in 14,820 cases collected from literature; it is dependent upon amount of infection which remains in the body; low before second and after seventh week, highest from fourth to sixth week.

_Prognosis._—Better in cases having severe diarrhea in first stage.

_Complications and sequelæ._—Abortion, menstrual disturbances, pneumonia, pleurisy, peritonitis.

FIG. 48.—Section through a rat’s muscle; the infected muscle fiber has
lost its striation, its nuclei are enlarged and increased in number.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212B.)

FIG. 49.—Portion of an isolated trichina cyst, at the pole of which
connective tissue cells have wandered into the thickened sarcolemma.
Greatly enlarged. (After Hertwig-Graham, see Braun, 1903, p. 284,
fig. 212C.)
]

_Clinical diagnosis._—Make microscopic examination:

(1) Of pork, if any has been left, to find encysted larvæ; if larvæ are found, feed pork immediately to two or three guinea pigs or _white_ rats, to determine if the encysted larvæ are alive; kill one rat after three days and examine intestinal content for adult; kill the second rat after two weeks, the third rat after three weeks, and hunt for larvæ in muscular portion of diaphragm. Even if live trichinæ are found in intestine, an examination of the muscles may show that the worms were too weak to reproduce, hence prognosis is favorable.

(2) Of patient’s blood, for increased proportion of eosinophiles.

(3) Of patient’s stools, for discharged adult worms, especially if diarrhea is severe; dilute the fecal matter with warm water and pour off whatever floats; place remainder in a shallow glass dish so that it will not be over one-twelfth of an inch deep; move the dish gently around over a dark background (such as dark paper), and hunt for small hair-like objects; place these, if found, in a drop of water on a slide, cover with a cover slip, and examine under low power. Or, if necessary, make a microscopic examination.

(4) Of small excised portion of patient’s deltoid, about three to four weeks after infection, for encysted larvæ; cut a small piece parallel to muscle fibers, tease this on a slide, add a drop of pure water, or water and glycerine, cover with another slide, flatten gently by pressure while examining under low power.

FIG. 50.—Calcified trichinæ in uncalcified cysts, from pork. Enlarged.
(After Ostertag, see Braun, 1903, p. 285, fig. 213.)
]

Suspect trichinosis especially under following circumstances: Several patients in same family or in same neighborhood, usually of North German descent, show typhoid-like symptoms shortly after a celebration (wedding, birthday party, etc.) at which pork was served.

FIG. 51.—Three phases of calcification of trichinæ and their cysts,
the changes starting from the poles of the cysts. Enlarged. (After
Ostertag, see Braun, 1903, p. 285, fig. 214.)
]

_Differential diagnosis._—Consider especially typhoid fever and rheumatism.

_Treatment._—Purge in early stage to carry away the adult worms and thus eventually decrease the amount of muscular infection. No treatment is known which can be relied upon to kill the larvæ in the muscles; benzine has been suggested. Stimulants may be given to carry patients through until the larvæ encyst.

PROPHYLAXIS.—_Kill off rats and mice._—Educate public to eat pork only when thoroughly cooked or thoroughly cured. A practical test of cooking is the white color of the meat on being cut; if the cut surface is reddish and serous, the pork is not sufficiently cooked to kill trichinæ.

As a matter of practical experience, the microscopic inspection of pork has not given the protection it is generally supposed to give. Of 6,329 cases with 318 deaths reported for Germany during the years 1881–1898, 3,388 cases with 132 deaths are directly attributable to faults in the inspection. This system directly increases the tendency to eat raw pork, gives the public a false sense of security, and does not give practical results commensurate with its expense.

ACANTHOCEPHALA—THORN-HEADED WORMS.

Genus GIGANTORHYNCHUS Hamann, 1892.

GENERIC DIAGNOSIS.—_Acanthocephala, Gigantorhynchidæ_: Large worms
with annulate round to flat, tape-like body. Hooks with 2 roots and
completely covered with transparent chitin. Proboscis sheath a
muscular apparatus, without cavity. Central nervous system caudad of
equator of proboscis sheath and eccentric. Lemnisci long, cylindrical,
with central canal.

TYPE SPECIES.—_Gigantorhynchus echinodiscus_ (Diesing, 1851).

The Moniliform Thorn-headed Worm—GIGANTORHYNCHUS MONILIFORMIS

(Bremser, 1819).

[Figs. 52 to 58.]

SPECIFIC DIAGNOSIS.—_Gigantorhynchus_ (p. 108): Body attenuated
anteriorly, with fine transverse striæ or rings, or even constrictions
which give the appearance of a series of beads, except in the caudal
fourth of body, which is nearly smooth and cylindrical. Proboscis 425
to 450μ long, 176 to 190μ in diameter, armed with feeble, very curved,
26μ long, hooks arranged more or less in quincunx and forming at most
15 transverse and about 12 longitudinal rows. Lemnisci more than a
centimeter in length, cylindrical, undulated posteriorly.

Male: Length 4 to 4.5 centimeters long; bursa campaniform.

Female: Length 7 to 8 centimeters (to 27 centimeters after Westrumb).

Eggs: Ellipsoidal, 85 by 45μ; external envelope thin, yellowish;
middle envelope very thick, colorless, homogeneous; inner envelope
less thick, colorless, and quite pliant. Embryo striated transversely
in posterior two-thirds, and covered with spines which increase in
size toward anterior end of embryo, the anterior spines being
transformed into hooklets with prong and base.

Development: With beetles (_Blaps mucronata_) as intermediate host.

HABITAT.—Small intestine of various small mammals; brown rat (_Mus
decumanus_); white rat (_Mus norvegicus albus_); _M. fuscirostris_;
hamster (_Cricetus frumentarius_); dormice (_Myoxus quercinus_ or
_glis_); field mole (_Arvicola arvalis_ or _agrestris_?); _Lemnus
arvalis_; and _Mustela putorius_. It can also develop in man, as has
been shown experimentally by Grassi and Calandruccio (1888, 521–525).

MEDICAL SIGNIFICANCE.—Grassi and Calandruccio report a doubtful case of infection in a girl near Catania. Calandruccio infected himself experimentally by swallowing the young worms taken from a Blaps. Twenty days later he was seized with severe pains which increased on pressure; diarrhea followed, with ringing in the ears, fatigue, and somnolence. Seventeen days later the characteristic eggs were found in his stools, and twelve days later the symptoms became so severe that he took 8 grams of extract of male fern; one to two hours later he passed 53 of the parasites. For two days the symptoms continued, on the second day fever developed, but all symptoms disappeared on the third day.

FIG. 52.—_Gigantorhynchus moniliformis_, female. ×2. (After Grassi &
Calandruccio, 1888, p. 523, fig. 1.)

FIG. 53.—_G. moniliformis_, male. ×2. (After Grassi & Calandruccio,
1888, p. 523, fig. 2.)

FIG. 54.—Rostellum of _G. moniliformis_. Greatly enlarged. (After
Grassi & Calandruccio, 1888,
p. 523, fig. 3.)

FIG. 55.—Hooks from same. Greatly enlarged. (After Grassi &
Calandruccio, 1888, p. 523, fig. 4.)

FIG. 56.—Eggs of _G. moniliformis_, with embryo. Greatly enlarged.
(After Grassi & Calandruccio,
1888, p. 523, fig. 5.)

FIG. 57.—Egg very greatly enlarged. (After Grassi & Calandruccio,
1888, p. 524, fig. 6.)

FIG. 58.—A young larva of _G. moniliformis_ in a _Blaps_; the
rostellum is invaginated and the larva is
surrounded by a thick inner jelly-like and thin outer cuticular
covering. Enlarged. (After Grassi &
Calandruccio, 1888, p. 524, fig. 7.)
]

ARACHNOIDEA.

Genus LINGUATULA Frœhlich, 1789.—Tongue worms.

Species LINGUATULA SERRATA Frœhlich, 1789.

The larva of this parasite is found encysted in the entrails of rabbits, cattle, and certain other animals, and it becomes mature in the nasal cavities of canines.

Both the larva and the adult have been reported for man, and the larva has been reported as occurring in _Mus decumanus_.

As canines are not fond of eating rats, the presence of the larval tongue worm in the latter is of more academic interest than practical importance, and although the theoretical possibility must be admitted that a dog by eating rats might become infected with tongue worms and eventually might transmit the infection to man, these possibilities seem somewhat remote. Remote possibilities must also be admitted to the effect that if a person ate a rat infected with tongue worms this person might become infected.

COMPENDIUM OF ANIMAL PARASITES REPORTED FOR RATS AND MICE (GENUS MUS).

By CH. WARDELL STILES, Ph. D., _Public Health and Marine-Hospital
Service_,

and

ALBERT HASSALL, M. R. C. V. S., _Assistant, Division of Zoology, United
States Bureau of Animal Industry_.

The following list of parasites is prepared from the detailed host catalogues of the zoological divisions of the Public Health and Marine-Hospital Service and the Bureau of Animal Industry.

The species of hosts and parasites are taken as given by the various authors. It is needless to say that no list of this kind can ever lay claim to being complete.

Genus MUS Linneaus, 1758.

[_Mus musculus_ should be the type species.]

MUS AGRARIUS.—Harvest Mouse.

CESTODA:

_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]

NEMATODA:

_obvelata_: Oxyuris.—Intestine.

ARACHNOIDEA:

_acuminatus_ Neumann: Ixodes.—External.

INSECTA:

_fasciatus_ Bosc: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla.—External.

MUS ALBIPES.

INSECTA:

_pallidus_ Taschenberg: Pulex.—External.

MUS ALEXANDRINUS.—Roof Rat.

[See also _Mus rattus alexandrinus_.]

CESTODA:

_diminuta_ Rudolphi, 1819: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_leptocephala_: Tænia.—Small intestine.
_murina_ Dujardin: Hymenolepis.—Small intestine. [See fraterna.]

MUS ALEXANDRINUS ALBIVENTRIS.

CESTODA:

_diminuta_ Rudolphi: Hymenolepis.—Small intestine.

MUS AMPHIBIUS.

_Dubium_ Rudolphi.—Inguinal gland.

CESTODA:

_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.

NEMATODA:

_nodosus_: Trichocephalus.—Cecum.
_obvelata_: Ascaris.

MUS ARVALIS.

CESTODA:

_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_longicollis_: Cysticercus.
_omphalodes_ Hermann: Tænia, Anoplocephala.—Intestine.

NEMATODA:

_nodosus_: Trichocephalus.
_obvelata_: Ascaris.

ACANTHOCEPHALA:

_moniliformis_: Echinorhynchus.

MUS BARBARUS.

[See also _barbatus_ Enderl.]

INSECTA:

_spiculifer_ Gerv.: Hæmatopinus, Polyplax.—External.

MUS BRASILIENSIS Geoffr.

[See also _Holochilus brasiliensis_.]

CESTODA:

_pisiformis_ Zeder: Cysticercus.

NEMATODA:

_muris brasiliensis_ Diesing: Physaloptera.
_obvelata_ Bremser: Oxyuris.

MUS CAPENSIS.

CESTODA:

_muris capensis_: Tænia.—Intestine.

NEMATODA:

_contortus_ Rudolphi: Trichocephalus.—Cecum.

MUS CRICETUS.

CESTODA:

_straminea_ Gœze: Tænia.—Intestine.

MUS DECUMANUS Pallas.—Brown or Norway Rat; German Wanderratte.

PROTOZOA:

? _balfouri_: Hæmogregarina.—Blood.
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See duodenalis.]
_lewisi_ Saville-Kent: Herpetomonas, Trichomonas, Trypanosoma.—Blood.
species Siebold: Sarcocystis.—Muscles.

TREMATODA:

_armata_: Cercaria.
_muris_: Distomum.
_spiculator_ Dujardin, 1845: Distoma, Echinostoma, Distomum,
Echinostomum.—Small intestine.

CESTODA:

_brachydera_ Diesing: Tænia.—Small intestine.
_contracta_ Janicki: Hymenolepis.—Intestine.
_crassa_ Janicki: Hymenolepis.—Intestine.
_diminuta_ Rudolphi: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_horrida_ Linstow, 1901: Tænia, Hymenolepis.—Intestine.
_microstoma_ Dujardin: Tænia, Hymenolepis.—Small intestine.
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Small intestine. [See
fraterna.]
_nana_ Siebold: Hymenolepis.—Small intestine. [See fraterna, murina.]
_pusilla_ Gœze: Tænia, Catenotænia.—Small intestine.
_ratti_: Tænia.—Intestine.
_relicta_ Zschokke, 1888: Tænia, Hymenolepis.—Small intestine.
species Janicki: Hymenolepis.
species: Hymenolepis.—Small intestine.

NEMATODA:

_annulosum_ Dujardin: Trichosoma, Trichosomum, Calodium.—Duodenum,
small intestine.
_anulosum_ see annulosum Dujardin: Trichosoma.
_circumflexa_ Polonio: Trichina.—Encysted in peritoneum.
_crassicauda_ Bellingham, 1840: Trichodes, Trichosoma.—Urinary
bladder, ureter, kidneys, intestine.
_hepaticum_ Bauer: Trichosoma.—Liver.
_hepaticum_ Railliet, 1891: Trichosoma.—Liver.
_hepaticus_ Bancroft: Trichocephalus.—Liver.
_longus_ Grassi & Segrè: Strongyloides, Rhabdonema.—Intestine.
_minimum_ Molin: Gongylonema.
_murina_ Leuckart: Spiroptera.—Stomach. [See obtusa.]
_muris_ Gmelin: Filaria.—Stomach.
_obtusa_ Rudolphi: Filaria, Spiroptera.—Stomach. [See murina.]
_obvelata_ Bremser: Oxyuris.—Large intestine.
_papillosum_ Polonio: Trichosoma.—Urinary bladder.
_rhytipleuritis_ Deslongchamps: Filaria.—Stomach.
_schmidtii_ Linstow: Trichosoma.—Urinary bladder.
species Davaine: Filaria [embryo].—Blood.
species: Heterakis.—Large intestine.
species undetermined: Oxyuris.
species Gerstæcker: Spiroptera.—Encapsuled in wall of stomach and
intestine.
species Bakody: Spiroptera.—Encapsuled in walls of alimentary canal
and muscles.
species: Spiroptera.—Encapsuled in wall of stomach and intestine.
species Parona: Strongyloides.
species Lutz, 1894: Strongylus.—Small intestine.
? species Railliet: Trichosoma.
_spiralis_ Owen, 1835: Trichina, Trichinella.—Adult in intestine,
larva in muscles.
_spumosa_ Schneider: Heterakis.—Cœcum and large intestine.
? _tenuissimum_ Leidy, 1891: Trichosomum.—Liver. [See hepaticum.]

ACANTHOCEPHALA:

_moniliformis_ Bremser: Echinorhynchus, Gigantorhynchus.

ARACHNOIDEA:

_agilis_ Koch: Lælaps.—External [See echidninus, musculi.]
_alepis_ Railliet & Lucet, 1893: Sarcoptes, Notoedres.—External, ears,
genitalia.
_complanatus_ Kramer: Gamasus.—External. [See stabularis, fenilis.]

_decumani_ Tiraboschi: Myonyssus.
_echidninus_ Berlese: Lælaps.—External.
_ensifera_ Poppe: Myobia.—External.
_fenilis_ Mègnin: Gamasus.—[See stabularis, complanatus.]
_musculi_ Schrank: Pediculus, Myobia.—External, head.
_musculi_ Mègnin: Hæmomyson.—External. [See echidninus, agilis.]
_musculi_ Schrank: Myobia.—External.
_ricinus_ Linné: Acarus, Ixodes.—External. [See rufus, sulcatus,
sciuri.]
_rufus_ Koch: Ixodes.—External. [See ricinus.]
_sciuri_ Koch: Ixodes.—External. [See ricinus.]
sp. n. Banks: Lælaps.—External.
_stabularis_ Koch: Gamasus, Hypoaspis, Lælaps.—External. [See
complanatus, fenilis.]
_sulcatus_ Koch: Ixodes.—External. [See ricinus.]
_tænioides_ Lamark (larva): Linguatula. [See serrata.]

INSECTA:

_acanthopus_ Denny: Hæmatopinus, Hoplopleura.—External.
_bidentatiformis_ Wagner: Neopsylla.—External.
_brasiliensis_ Baker: Pulex.—External.
_canis_ Curtis: Ctenocephalus, Ceratophyllus.—External.
_cheopis_ Roth.: Pulex, Læmopsylla.—External.
_consimilis_ Wagner: Ceratophyllus.—External.
_fasciatus_ Bosc: Pulex, Ceratophyllus. External.
_felis_ Bouché: Ctenocephalus.—External.
_irritans_ Linné: Pulex.—External.
_lagomys_ Wagner: Ceratophyllus.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsylla.—External.
_mustelæ_ Wagner: Ceratophyllus.—External.
_penicilliger_ Grube: Ceratophyllus.—External.
_philippinensis_ Herzog: Pulex.—External.
_serraticeps_ Gervais: Pulex.—External.
_spinulosus_ Burmeister: Hæmatopinus, Polyplax.—External.

MUS DECUMANUS × MUS NORVEGICUS ALBUS.

PROTOZOA:

undetermined.—Small intestine.

CESTODA:

_fasciolaris_: Cysticercus.—Liver.
species: Hymenolepis.—Intestine.

NEMATODA:

_spiralis_ Owen: Trichinella.—Artificial infection.

MUS DOMESTICUS = MUS MUSCULUS ALBUS.

ARACHNOIDEA:

_crotali_ Humboldt (larva): Porocephalus.—Encysted in various organs,
experimental.

MUS FERCULINUS.

INSECTA:

_thomasi_ Rothschild: Stephanocircus.—External.

MUS FLAVIDUS.

CESTODA:

? _gracilis_ Janicki: Davainea.—Intestine.

MUS FULIGINOSUS.

ARACHNOIDEA:

_crotali_ Humboldt: Porocephalus.—Encysted in various organs.

MUS FURCIROSTRIS Wagner.

ACANTHOCEPHALA:

_moniliformis_ Bremser: Echinorhynchus.—Intestine.

MUS GENTILIS.

INSECTA:

_cheopis_ Rothschild: Pulex.—External.

MUS LEMMUS.

CESTODA:

_lemmi_: Tænia.—Intestine. [See muris lemmi.]
_muris lemmi_: Tænia.—Intestine. [See lemmi.]

MUS MEYERI.

CESTODA:

_celebensis_ Janicki, 1902: Davainea.—Intestine.

MUS MINIMUS Ptrs.

NEMATODA:

species Linstow, 1901: Spiroptera.—Stomach.

MUS MINUTUS Pallas.—German Zwergmaus.

NEMATODA:

_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris.—[See obvelata.]

MUS MUSCHENBROCKI.

CESTODA:

_polycalceola_ Janicki: Davainea.—Intestine.

MUS MUSCULUS[AC] Linné, 1758.—House Mouse.

Footnote AC:

In laboratory experiments the white mouse is used more than the
ordinary form, but the host is frequently reported simply as “the
mouse.”

——:

_Dubium_ Rudolphi, 1819.—Inguinal gland.

PROTOZOA:

_brucei_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_dimorphon_: Trypanosoma, Trypanozoon.—Blood.
_duttoni_ Thiroux, 1905: Trypanosoma, Trypanozoon.—Blood.
_equinum_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_equiperdum_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_evansi_: Trypansoma, Trypanozoon.—Blood, artificial infection.
_falciforme_ Schneider: Coccidium, Eimeria.—Intestine.
flagellate, something like Herpetomonas bütschlii.
_gambiense_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_intestinalis_ Lambl, 1859: Lamblia, Megastoma.—Intestine. [See
duodenalis, muris.]
_muris_ Grassi: Amœba.
_muris_ Bensen, 1908: Lamblia.—Intestine. [See intestinalis.]
_muris_ Schuberg: Coccidium.—Intestine.
_muris_ Smith & Johnson, 1902a: Klossiella.—Renal epithelium.

_muris_ Balfour: Leucocytozoon.—Blood.
_muris_ R. Blanchard: Miescheria, Sarcocystis.—Striated muscle.
_musculi_ Kendall: Trypanosoma.—Blood.
_schubergi_ Labbé: Pfeifferella.—Intestine.
species Th. Smith: Eimeria.—Kidney.
species J. J. Clarke: Pfeifferella.—Intestine.
species Miescher: Sarcocystis.—Muscles.
_stercorea_ Cienkowski: Chlamydophrys.—Intestine.

TREMATODA:

_armata_: Cercaria.
_muris_ Ercolani, 1882: Distomum.
_musculi_ Rudolphi, 1819: Distoma, Distomum.—Intestine.
_recurvum_ Dujardin, 1845: Distoma, Distomum.—Intestine.

CESTODA:

_canis lagopodis_ Viborg: Tænia.—Intestine. [See lineata.]
_contracta_ Janicki: Hymenolepis.—Intestine.
_crassa_ Janicki, 1904: Hymenolepis.—Intestine.
_diminuta_ Rudolphi: Tænia, Hymenolepis.—Intestine.
_echinococcus._ [See Devé, 1904, October 28; 264.]
_fasciolaris_ Rudolphi, 1819: Cysticercus.—Liver.
_imbricata_ Diesing: Tænia.—Small intestine.
_leptocephala_ Creplin, 1849: Tænia.—Small intestine.
_lineata_ Gœze: Tænia, Mesocestoides, Ptychophysa. [See canis
lagopodis.]
_microstoma_ Dujardin, 1845: Tænia.—Intestine.
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Intestine. [See
fraterna.]
_muris capensis_: Tænia.
_muris hepatica_ Rœderer, 1762: Fasciola.—Liver. [See fasciolaris.]
_musculi_ Rudolphi, 1810: Tænia.—Abdominal cavity.
_pisiformis_ Zeder: Cysticercus.—Liver.
_pusilla_ Gœze, 1782: Tænia.—Intestine.
species Janicki: Hymenolepis.—Intestine.
species Merrem, 1781: Fasciola.—Liver. [See fasciolaris.]
_tenella_ Pallas, 1781 pars: Tænia.—Abdominal cavity. [See musculi.]
_umbonata_ Molin, 1858: Tænia.—Intestine.

NEMATODA:

_bacillatum_ Eberth: Trichosoma.—Esophagus.
_hepaticum_ Railliet, 1889: Trichosoma.—Liver.
_minimum_ Molin: Gongylonema.—On stomach, liver.
_muris_ Gmelin: Filaria.
_muris_ Werner: Lumbricus, Ascaris, Fusaria. [See obtusa Frœlich.]
_muris musculi_ Creplin, 1849: Trichosoma.—Large intestine.
_musculi_ Rudolphi: Filaria, Gongylonema.—Abdomen.
_nodosus_ Rudolphi: Trichocephalus.—Intestine, cecum.
_oxyura_ Nitzsch, 1821: Ascaris.—[See obvelata.]
_obvelata_ Rudolphi: Oxyuris.—Cecum.
_obtusa_ Rudolphi: Filaria, Spiroptera.—Stomach.
_obtusa_ Frœlich, 1791: Ascaris.—Stomach. [See muris Werner.]
_quadrialata_ Molin: Spiroptera.—Stomach.
_semilanceolata_ Molin, 1858: Oxyuris.—Cecum. [See tetraptera.]
_spiralis_ Owen, 1835: Trichina, Trichinella.—Adult in intestine,
larva in muscles.
_tetraptera_ Nitzsch: Oxyuris.—Cecum. [See semilanceolata.]
_tricuspis_ Leuckart: Ollulanus.—Muscles.

ACANTHOCEPHALA:

_muris_ Zeder: Echinorhynchus.—Stomach.

ARACHNOIDEA:

_coarctata_ Heyden: Myobia.—External. [See musculi Schrank.]
_musculi_ Oudemans: Demodex.—Hair follicles. [See folliculorum
musculi.]
_musculi_ Schrank: Pediculus, Myobia.—External, head.
_musculinus_ Galli-Valerio: Myocoptes.—External.
_simplex_ Tyrrell: Psorergates.—External.

INSECTA:

_acanthopus_ Burmeister, 1838: Hoplopleura, Hæmatopinus.—External.
_agyrtes_ Heller: Typhlopsylla.—External.
_assimilis_ Taschenberg: Typhlopsylla.—External.
_charlottensis_ Baker: Odontopsyllus.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla, Typhlopsylla.—External.
_serratus_ Burm., 1838: Hæmatopinus.—External.
_serraticeps_ Taschenberg: Ctenocephalus.—External.
larva of a dipteron, gen. sp.?
_taschenbergi_ Wagner: Ctenopsyllus.—External.
_tripectinata_ Tiraboschi: Hystrichopsylla.—External.
_walkeri_ Roth.: Ceratophyllus.—External.

MUS MUSCULUS ALBUS.—White Mice.

CESTODA:

_fasciolaris_ Rudolphi: Cysticercus.—Liver.

ARACHNOIDEA:

_crotali_ Humboldt (larva): Porocephalus.—Encysted in various organs.
_proboscideum_: Pentastomum. [See crotali.]

MUS NAVALIS.

NEMATODA:

_labiodentata_ Linstow: Spiroptera.—Intestine.

MUS NORVEGICUS Erxl.—Norway Rat.

[See also _Mus decumanus_.]

PROTOZOA:

_lewisi_: Trypanosoma, Trypanozoon.—Blood.

INSECTA:

_bidentatiformis_ Wagner: Ctenophthalmus.—External.
_brasiliensis_ Baker: Pulex.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_murinus_ Tiraboschi: Pulex.—External.
_musculi_ Dugès: Ctenopsyllus.—External.

MUS [NORVEGICUS] ALBUS.—White Rat.

PROTOZOA:

_muris_ Fantham: Piroplasma.—Blood.
_perniciosum_ Miller: Hepatozoon.—Liver, blood.

CESTODA:

_fasciolaris_ Rudolphi: Cysticercus.—Liver.

NEMATODA:

_hepaticum_: Trichosoma.—Liver.
_spiralis_ Owen, 1835: Trichinella.—Adult in intestine, larva in
muscle.

ARACHNOIDEA:

_ensifera_ Poppe: Myobia.

MUS PUMILIS Dujardin.—Little Mouse.

CESTODA:

_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Intestine. [See
fraterna.]

MUS PYRRHORHINUS Neuwied.

[See also _Hesperomys pyrrhorhinus_.]

CESTODA:

_diminuta_: Tænia.—Intestine.

ARACHNOIDEA:

_crotali_ Humboldt: Porocephalus.—Encysted in various organs.
_subcylindricum_: Pentastomum.—Liver.

MUS RAJAH.

CESTODA:

_blanchardi_ Parona: Davainea.

MUS RATTUS Linné.—German Hausratte.

PROTOZOA:

“amibes.”
_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See duodenalis,
muris.]
_lewisi_ Saville-Kent, 1880: Trypanosoma.—Blood.
species Siebold: Sarcocystis.—Muscles.

TREMATODA:

_spiculator_: Distomum.

CESTODA:

_cellulosæ_ Rudolphi: Cysticercus.—Peritoneum.
_diminuta_ Rudolphi, 1819: Tænia, Hymenolepis.—Small intestine.
_fasciolaris_ Rudolphi: Cysticercus.—Liver.
_microstoma_ Dujardin: Tænia, Hymenolepis.—Small intestine.
_minima_: Tænia. [See diminuta.]
_murina_ Dujardin, 1845: Tænia, Hymenolepis.—Small intestine. [See
fraterna.]
_pusilla_ Gœze, 1782: Tænia, Catenotænia.—Small intestine.
_ratti_ Rudolphi: Tænia.—Small intestine.
_ratticola_ Linstow: Bothriocephalus.—Liver.
species Eber: Tænia.—Intestine.
_umbonata_ Molin: Tænia.—Intestine.
_varesina_ Parona: Tænia.—[See diminuta.]

NEMATODA:

_annulosum_ Dujardin: Trichosoma, Calodium.—Intestine.
_anulosum_: Trichosoma. [See annulosum.]
_brauni_ Linstow: Spiroptera.
_circularis_ Linstow: Physaloptera.—Stomach.
_circumflexa_ Polonio: Trichina.—Encysted in peritoneum.
_nodosus_ Rudolphi: Trichocephalus.—Cecum.
_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris. [See obvelata.]
_ratti_ Diesing: Spiroptera.—Urinary bladder.
_rhytipleuritis_ Deslongchamps: Filaria.—Stomach.
species Gerstæcker: Spiroptera.—Wall of stomach and intestine.
species Bakody: Spiroptera.—Encapsuled in wall of intestine, muscles.
_spumosa_ Schneider: Heterakis.—Cecum, colon.

ACANTHOCEPHALA:

_moniliformis_ Bremser: Echinorhynchus, Gigantorhynchus.—Intestine.

ARACHNOIDEA:

_ægyptium_ Linné: Acarus, Ixodes, Hyalomma.—External. [See
marginatum.]
_agilis_ Koch: Lælaps.—External. [See echidninus, musculi.]
_alepis_ Railliet & Lucet, 1893; Sarcoptes, Notoedres.—External, ears,
genitalia.
_echidninus_ Berlese: Lælaps.—External. [See agilis, musculi.]
_marginatum_ Koch: Hyalomma.—External. [See ægyptium.]
_muris_ Can., 1894: Notoedres.—External. [See alepis.]
_musculi_ Mègnin: Hæmomyson.—External. [See agilis, echidninus.]
_serratum_: Pentastomum.—Thoracic cavity.

INSECTA:

_brasiliensis_ Baker: Pulex.—External. [See cheopis.]
_cæcata_ Enderlein: Dermatophilus, Rhynchoprion.—External.
_cheopis_ Rothschild, 1903: Lœmopsylla.—External. [See brasiliensis,
murinus, pallidus, philippinensis.]
_fasciatus_: Ceratophyllus.—External.
_gallinacea_ Westwood: Echidnophaga, Argopsylla.—External.
_irritans_ Linné: Pulex.—External.
_italicus_ Tiraboschi: Ceratophyllus. External.
_londiniensis_ Rothschild: Ceratophyllus.—External.
_mexicanus_ Baker: Ctenopsyllus.—External.
_murinus_ Tirab.: Pulex.—External. [See cheopis, pallidus,
brasiliensis, philippinensis.]
_musculi_ Dugès: Ctenopysllus.—External.
_pallidus_ Taschenberg: Pulex.—External. [See brasiliensis, cheopis,
murinus, philippinensis.]
_philippinensis_ Herzog: Pulex.—External. [See brasiliensis, cheopis,
murinus, pallidus.]
_rhynchopsylla_ Tiraboschi: Echidnophaga.—External.

MUS RATTUS ALEXANDRINUS.

[See also _Mus Alexandrinus_.]

INSECTA:

_brasiliensis_ Baker: Pulex.—External.
_cæcata_ End: Dermatophilus.—External.
_canis_ Curtis: Ctenocephalus.—External.
_cheopis_ Roth.: Pulex.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_felis_ Bouché: Ctenocephalus.—External.
_gallinacea_ Westwood: Echidnophaga.—External.
_irritans_ Linné: Pulex.—External.
_londiniensis_ Roth.: Ceratophyllus.—External.
_murinus_ Tiraboschi: Pulex.—External.
_musculi_ Dugès: Ctenopsylla.—External.
_philippinensis_ Herzog: Pulex.—External.
_rhynchopsylla_ Tiraboschi: Echidnophaga, Argopsylla.—External.

MUS RUFESCENS Gray.

PROTOZOA:

_lewisi_ Saville-Kent, 1880: Trypanosoma, Trypanozoon.—Blood.

MUS SIPORANUS.

CESTODA:

_blanchardi_ Parona: Davainea.—Intestine.

MUS SURIFER.

NEMATODA:

_muricola_: Spiroptera.—Subcutaneous.

MUS SYLVATICUS Linné.—German Waldmaus.

TREMATODA:

_recurvum_ Dujardin, 1845: Distoma, Distomum, D.
(Brachylaimus).—Intestine.
_vitta_ Dujardin, 1845: Distoma, Distomum, D.
(Brachylaimus).—Intestine.

CESTODA:

_muris sylvatici_ Rudolphi: Tænia.—Intestine.
_pusilla_ Gœze: Tænia.—Intestine.

NEMATODA:

_cristatum_ Rudolphi: Ophiostomum, Rictularia.—Intestine.
_lævis_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_minutus_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_muris sylvatici_ Dujardin: Trichosoma.—Intestine.
_nodosus_ Rudolphi: Trichocephalus.—Intestine, cecum.
_obtusa_ Rudolphi: Spiroptera.
_obvelata_ Bremser: Oxyuris.—Cecum.
_oxyura_ Nitzsch, 1821: Ascaris. [See obvelata.]
_polygyrus_ Dujardin: Strongylus, Metastrongylus.—Intestine.
_spirogyrus_ Leuckart: Strongylus.—Intestine.
_stroma_ Linstow, 1884: Oxyuris.—Intestine.
_tetraptera_ Nitzsch: Oxyuris.—Intestine.

ARACHNOIDEA:

_simplex_ Tyrell: Psorergates.—Skin.

INSECTA:

_agyrtes_ Heller: Ctenophthalmus, Typhlopsylla.—External.
_assimilis_ Taschenberg: Typhlopsylla.—External.
_fasciatus_ Bosc: Ceratophyllus.—External.
_gallinæ_ Schrank: Ceratophyllus.—External.
_italicus_ Tiraboschi: Ceratophyllus.—External.
_londiniensis_ Rothschild: Ceratophyllus.—External.
_musculi_ Dugès: Ctenopsyllus, Ctenopsylla.—External.
_obtusiceps_ Ritsema: Hystrichopsylla.—External.
_pentacanthus_ Rothschild: Neopsylla, Ctenophthalmus.—External.
_poppei_ Wagner: Typhloceras, Typhlocerus.—External.
_proxima_ Wagner: Typhlopsylla, Ctenopthalmus.—External.
_talpæ_ Curtis: Hystrichopsylla.—External.
_taschenbergi_ Wagner: Ctenopsylla.—External.

MUS SYLVESTRIS.

PROTOZOA:

_intestinalis_ Lambl, 1859: Lamblia.—Intestine. [See muris.]

MUS TECTORUM Sari.

CESTODA:

_fasciolaris_: Cysticercus.—Liver.

MUS VARIEGATUS.

CESTODA:

_muris variegati_ Janicki: Hymenolepis.—Intestine.
_trapezoides_ Janicki: Davainea.—Intestine.

MUS VELUTINUS Balser, 1905.

INSECTA:

_dasyuri_ Skuse: Stephanocircus.—External.
_hercules_ Roth.: Macropsylla.—External.
_simpsoni_ Rothschild: Stephanocircus.—External.
_simsoni_. [See simpsoni.]

MUS in the sense of “rats.”

The following parasites are reported either from “rats” or from “_Mus_” in the sense of “rats:”

PROTOZOA:

_brucei_: Trypanosoma, Trypanozoon.—Blood.
_dimorphon_: Trypanosoma, Trypanozoon.—Blood.
_equiperdum_: Trypanosoma, Trypanozoon.—Blood.
_evansi_: Trypanosoma, Trypanozoon.—Blood.
_evansii_: Trypanosoma. [See evansi.]
_gambiense_: Trypanosoma, Trypanozoon.—Blood, artificial infection.
_intestinale_ R. Blanchard, 1885: Megastoma.—Intestine. [See muris.]
_muris_ Grassi: Amœba.

CESTODA:

_fasciolaris_: Cysticercus.

NEMATODA:

_hepaticum_ Railliet, 1889: Trichosoma.—Liver.
_hepaticus_: Trichocephalus.
species Davaine: Filaria.—Blood.

GORDIACEA:

_Gordius._ By error Cerruti & Camerano (1888b, 6) have interpreted a
title by
Leidy (1879) as meaning that he found _Gordius_ in a rat.

ARACHNOIDEA:

_sanguineus_ Latreille: Rhipicephalus.—External.

INSECTA:

_capitis_ Nitzsch: Pediculus.—External.
_canis_ Curtis: Ctenocephalus.—External.
_præcisus_: Hæmatopinus.—External.

MUS species.

Under various “_Mus_ sp.” entries, the following parasites are
reported:

PROTOZOA:

_gambiense_: Trypanosoma.—Blood, artificial injection.

INSECTA:

_aganippes_ Roth.: Ctenopsylla.—External.
_agyrtes_ Heller: Typhlopsylla.—External.
_colossus_ Roth.: Pygiopsylla.—External.
_ellobius_ Roth.: Ctenopsylla.—External.
_hercules_ Roth.: Macropsylla.—External.
_miacantha_: Polyplax.—Hair.
_pinnatus_ Wagn.: Ceratophyllus.—External.
_præcisus_ Neum., 1902: Hæmatopinus.—External.

WATER RAT.

[See also _Mus amphibius_.]

CESTODA:

_longicollis_: Cysticercus.—Axillary space.

INSECTA:

_spiniger_ Burm., 1838: Hæmatopinus.

MUS.

The following parasites are recorded under “_Mus._:”

PROTOZOA:

_falciformis_: Eimeria.—Intestine.

TREMATODA:

_migrans_: Dist.

CESTODA:

_blanchardi_ Parona: Davainea.
_celebensis_ Janicki: Davainea.
_gracilis_ Janicki: Davainea.
_muris variegati_ Janicki: Hymenolepis.
_nana_ Siebold: Hymenolepis. [See fraterna.]
_polycalceola_ Janicki: Davainea.
_relicta_ Zschokke: Hymenolepis.
_trapezoides_ Janicki: Davainea.

NEMATODA:

_hepaticum_ Railliet: Trichosoma.
_obvelata_ Bremser: Oxyuris.—Intestine.

ARACHNOIDEA:

_musculi_ Oudemans: Demodex.

INSECTA:

_cheopis_ Roth.: Lœmopsylla.—External.
_felis_ Bouché: Ctenocephalus.

MUS.—A Field Mouse.

CESTODA:

_longicollis_: Cysticercus.—Thoracic cavity.

THE FLEA AND ITS RELATION TO PLAGUE.

By Passed Assistant Surgeon CARROLL FOX,

_United States Public Health and Marine-Hospital Service_.

THEORIES AS TO TRANSMISSION OF PLAGUE.

1. Direct contagion from man to man.

2. Through slight abrasions of the skin, mucous membranes of mouth,
tonsils, nose, and conjunctiva receiving contaminated material.

3. Through the respiratory tract, from air contaminated with dried
infectious sputum or dejecta. (Possibly the cause of primary pneumonic
plague.)

4. Through the alimentary tract from food contaminated with saliva or
excretions from plague patients, or dejecta or the feet of insects
that have fed on plague material. In the case of rats, from eating the
carcasses of infected rats.

5. Infected clothes, soil, or houses.

6. Through the bites of insects, especially the flea.

It has been noticed for many years that an epidemic of plague in man
was associated with an epizootic of high mortality among rats, but it
was not until Yersin discovered the _Bacillus pestis_ in 1894 that the
disease in man and rats was shown to be identical. The first five
theories are not satisfactory in explaining the epidemiology of
plague, and in 1897 Simond advanced the theory that plague was carried
by means of fleas. Hankin in 1898 also suggested an insect as an
intermediate host. This theory has been developed by Ashburton
Thompson, Gauthier and Raybaud, Liston, Verjbitski, and others, and
finally by the last Indian Plague Commission, whose work makes a
distinct advance in our knowledge of this subject. The reader is
referred to the work of this commission for a review of the subject,
which has been liberally used in the preparation of this paper.[AD]

Footnote AD:

Journal of Hygiene (Vol. VI, No. 4; Vol. VII, No. 3; Vol. VII, No.
6; Vol. VIII, No. 2).

INSECTS THAT HAVE BEEN SUSPECTED IN THE TRANSMISSION OF PLAGUE.

It is probable that all insects capable of sucking blood will take the
_Bacillus pestis_ into their alimentary canal if they feed on a
septicæmic plague animal. Ogata suggested that not only the flea but
the mosquito also may be responsible for the transmission of plague.
Yersin, Hankin, and Nuttall have each demonstrated the presence of
_Bacillus pestis_ in the dejecta of flies and ants; and Nuttall and
Verjbitski in the stomach and dejecta of the bedbug. Hertzog found the
bacilli in the _Pediculus capitis_ taken from a child which died of
plague, and McCoy[201] has found the organism in lice, _Hæmatopinus
columbianus_, taken from a plague-infected squirrel. The plague
bacilli have been frequently demonstrated in rat fleas taken from
plague rats, and McCoy has shown its presence in the flea
(_Ceratophyllus acutus_) of the California ground squirrel (_Citellus
beecheyi_). The cockroach has also been thought to be instrumental in
spreading the infection by contaminating food. The presence of bacilli
in the stomach and dejecta of insects has not only been proven
microscopically but by animal inoculation as well.

Assuming that the relation between rat plague and human plague has
been proven without a doubt—that is, that an outbreak of human plague
is associated with an infection in rats, or, in other words, that
plague is primarily a disease of rats and secondarily a disease of
man—the theory that it is conveyed through an intermediate parasitic
host is the only one which will fulfill all the requirements, and
after a study of their habits we are able to exclude all of the
parasites but the flea as the active agent in its transmission.

Plague is rarely or never contracted either in rat or in man by eating
contaminated food. Therefore those insects like flies and cockroaches,
which are supposed to spread the infection by contaminating food with
their dejecta, need not be considered.

The habits of the domestic mosquitoes are such that while they
occasionally do bite animals they usually feed on the blood of man,
and are not known to feed where there is much hair, as there is on the
rat. This also applies to the bedbug. Verjbitski has shown
experimentally that bedbugs would not feed on rats until the animals
were shaved.

Pediculi are degenerate insects, their powers of locomotion being
limited. Their eggs are laid on and are attached to the hair of the
host. They are born, live, and die on the same host, and rarely pass
from one animal to another of a different species. It can not be
denied, however, that this parasite occasionally may be instrumental
in spreading plague from rat to rat. The _Pediculus capitis_, if
placed on a rat, will feed with avidity, but these insects are rarely
found upon rats in nature.

We have no record of plague bacilli having been demonstrated in mites
commonly found on rats, but no doubt if search be made they could be
found after feeding on a septicæmic plague rat. These mites, however,
always confine themselves closely to their particular host and are not
known to bite man. The tiny itch mite (_Notoedres alepis_, Railliet
and Lucet) producing rat scabies has, according to Schumann,[202] been
known to cause a cutaneous lesion in man, but this mite need not be
considered from a plague standpoint.

The flea, on the other hand, lives but part of the time on its host,
its eggs developing in the nests or runs of the animal. Again, this
insect does not confine itself to one particular species of host only,
as frequently the flea of one animal is found on an animal of an
entirely different species. Unlike the lice, they are very active and
can readily move from place to place. Not only that, but it has been
frequently demonstrated that the fleas of rats and of other animals
would readily take to man, especially if their natural host was
scarce. That rat fleas will bite man has been demonstrated by Gauthier
and Raybaud, working with the _Leomopsylla cheopis_; Tidswell,
_Lœmopsylla cheopis_ and _Ceratophyllus fasciatus_; Liston,
_Lœmopsylla cheopis_; Tiraboschi, _Lœmopsylla cheopis_; Indian Plague
Commission, _Lœmopsylla cheopis_; and McCoy and Mitzmain[203],
_Lœmopsylla cheopis_, _Ceratophyllus fasciatus_, and _Ctenopsyllus
musculi_. It has generally been considered that the _Ctenopsyllus
musculi_, above all others, would not bite man, but the last-named
observers showed that it would occasionally feed, although it would
not live long, in captivity. One of the fleas, a _Ceratophyllus
fasciatus_, was kept alive by Mitzmain for over four months on man’s
blood alone.

EXPERIMENTS PROVING THAT FLEAS CAN TRANSMIT PLAGUE.

By a series of experiments carried out in specially constructed cages
and go-downs where healthy rats in the absence of fleas were brought
in contact with plague-infected rats, the Indian Plague Commission
showed that the healthy rats would not contract the disease,
notwithstanding the fact that they were not only in intimate contact
with the sick rats, but also with the contaminated food and excreta of
the sick rats. They then showed that if fleas were introduced the
healthy rats would contract plague, the rate of progress of the
epizootic being in direct proportion to the number of fleas present.
By hanging cages containing healthy rats in cages holding infected
rats, but above the jumping distance of a flea, it was shown that the
healthy rats would remain well, while those in cages hung within 2
inches from the ground would contract plague. Thus they excluded
aerial infection. They also found that if fleas were excluded young
rats could suckle a plague-infected mother without contracting the
disease.

Guinea pigs were allowed to run in houses where cases of human and of
rat plague were known to have occurred and where many fleas were
present. These rodents served as good traps for the fleas and 29 per
cent of them contracted plague.

Most of the experiments of the Indian Plague Commission were done with
the Indian rat flea, the _Lœmopsylla cheopis_, but they also performed
27 experiments with the cat flea, _Ctenocephalus felis_, with negative
results; 35 experiments with the human flea, _Pulex irritans_, 3 of
which were successful; and 2 experiments with the _Ceratophyllus
fasciatus_, the common rat flea of Europe and North America, both of
which were successful.

In San Francisco a few experiments under purely experimental
conditions have been carried on by McCoy to determine the ability of
the squirrel flea, the _Ceratophyllus acutus_, to transmit plague.
Fleas that had been previously fed on the blood of a septicæmic
plague-infected squirrel were then allowed to feed from test tubes on
healthy guinea pigs. While the feces of some of these fleas up to four
days, when inoculated into guinea pigs, were proven to be infective,
none of those guinea pigs on which the fleas were allowed to feed
contracted plague. It might be said, however, that in no case were
they seen to eject feces while feeding, the significance of which will
be apparent later.

THE BACILLUS IN THE FLEA.

The Indian Plague Commission found that the average capacity of the
rat flea’s stomach (_Leomopsylla cheopis_) was 0.5 cubic millimeter,
and that it might receive as many as 5,000 germs while imbibing blood
from a plague rat. They further found that the bacillus would multiply
in the stomach of a flea and that the percentage of fleas with bacilli
in the stomach varied with the season of the year. In the epidemic
season the percentage was greatest for the first four days, and on one
occasion the stomach was found filled with _Bacillus pestis_ on the
twentieth day. In the nonepidemic season no plague bacilli were found
in the stomach after the seventh day. They also found that in the
epidemic season fleas might remain infective up to fifteen days, while
in the nonepidemic season but seven days, and in the latter case the
percentage of infection in animals was much less than in the epidemic
season. They showed that while one flea was occasionally able to carry
the infection this was not usual. It was found that both the males and
the females were capable of transmitting the disease.

After a number of dissections they were unable to demonstrate the
presence of bacilli anywhere but in the stomach and rectum. At no time
was anything found in the body cavity or salivary glands and but
rarely in the œsophagus, and then only when the flea was killed
immediately after feeding.

We have in San Francisco examined quite a number of serial sections of
plague-infected fleas with the same result as obtained by the Indian
Plague Commission. The bacilli are readily demonstrated, sometimes in
enormous numbers, in the gizzard, stomach, and in the rectum, but at
no time have they been found in the body cavity, the salivary glands,
or the ovary. In fact, as we are dealing with a vegetable organism and
not an animal organism, like the _Plasmodium malariæ_, we could hardly
expect to find any biologic change, except simple multiplication,
occurring in the intermediate host.

HOW THE FLEA CLEARS ITSELF OF BACILLI.

Some explanation is necessary as to why the bacilli eventually
disappear from the flea, although they seem to multiply during the
first few days. It is evident that the peristaltic action of the
stomach during the course of digestion forcing the blood at the proper
time into the rectum, finally to be ejected from the body, would in
itself cause many bacilli to be discharged, but naturally a few would
remain to multiply indefinitely. The bacteriacidal action of the blood
is soon lost after entering the flea’s stomach, but it has been shown
by proper staining that the leucocytes after the first feeding with
healthy blood contain numbers of _Bacillus pestis_, and it seems
probable that this phagocytic action is important in the cleansing
process. It has been shown that after successive feedings on the blood
of noninfected animals the power of phagocytosis is increased, and
that successive feedings on the fresh blood of animals that have been
immunized against plague still further assists and hastens the
process. When there is a frequent introduction of fresh normal or
immunized blood its bactericidal action is also instrumental in the
cleansing process.

REGIONAL DISTRIBUTION OF FLEAS ON RATS.

The location of the primary bubo in a case of plague, human or rodent,
depends upon the site of inoculation, for that group of glands will
first enlarge which has direct lymphatic connection with the area
through which the _Bacillus pestis_ enters the animal organism. The
British Indian Plague Commission found that 72 per cent of their
naturally infected rats and 61 per cent of the rats experimentally
infected by fleas had cervical buboes, while in no instance in over
5,000 plague rats was a mesenteric bubo encountered. On the other
hand, where plague was induced through feeding healthy rats with the
carcasses of plague rats a mesenteric bubo was found in 74.5 per cent
of those infected and a cervical bubo in 36 per cent. In San Francisco
in naturally infected rats a primary mesenteric bubo has never been
seen, and a cervical bubo has been seen but once. These figures show
conclusively that naturally infected rats are not infected by feeding.
It is curious, as has been pointed out by McCoy[204], that such a
large percentage of cervical buboes should be found in India, while a
cervical bubo has been seen but once in naturally infected animals in
San Francisco. Here the axillary and inguinal buboes are the rule. The
Indian Commission found that the commonest situation to find fleas on
guinea pigs was the head and neck. They combed 53 guinea pigs to
determine the regional distribution of fleas, and found that 65.3 per
cent were taken from the neck and head. This would account for the
preponderance of cervical buboes in guinea pigs observed in their
work, and inferentially for the preponderance of cervical buboes found
in naturally infected rats. Thinking that the predominating rat flea
in San Francisco, the _Ceratophyllus fasciatus_, might be the carrier
of the infection and that it might prefer a different part of the body
than the _Lœmopsylla cheopis_, McCoy and Mitzmain carried on a series
of investigations to determine the regional distribution of fleas on
the rat’s body, but this has shown that while the _Ctenopsyllus
musculi_ seems to be generally confined to the head and neck, the
_Ceratophyllus fasciatus_ and _Lœmopsylla cheopis_ are almost
invariably taken from the body, especially from the pelvic region.

ANATOMY OF THE MOUTH PARTS OF THE CERATOPHYLLUS FASCIATUS.

The following description differs somewhat from that given by
Wagner[205] and the description found in the Journal of Hygiene, both
of which, however, refer to different species of Siphonaptera.

The mouth parts may be divided into those inside and those outside of
the head.

OUTSIDE THE HEAD.

The epipharynx, or pricker, is a long, slender, hollow organ. Its
cavity is closed distally, and proximally connects with the hoemocoel.
It is made up of a dorsal and a ventral portion. Its dorsal portion
ends just within the head. Its ventral portion is grooved and is
continuous with the posterior wall of the aspiratory pharynx. Its
distal extremity is slightly expanded, forming a stylet for piercing,
while the little papillæ seen along the anterior surface in many
species are absent in this one. Laterally there is a membranous
expansion which interlocks with a similar expansion on the mandibles,
forming a tube, through which the blood is sucked.

The mandibles are two in number, articulating just within the head, so
that they are capable, of independent movement. They are serrated at
their distal extremities. Above, within the head, the anterior portion
of the mandibles ends just behind the beginning of the hypopharynx, to
which it is connected, becoming practically continuous with that
organ. The posterior portion is attached to its basal element. Each
mandible contains a groove, forming practically a closed canal, which
becomes continuous with the exit duct of the salivary pump.

The rostrum (labial palpi) forms a protection and guide to the
mandibles and epipharynx. Its first portion is unpaired and
articulates within the head, with its basal element. At the apex of
its first portion it bifurcates, forming a paired organ, which is
divided into a varying number of pseudojoints, depending on the
species of the flea. As it is a chitinous structure, these
pseudojoints, areas in which there is little chitin, enable it to
double up as the mandibles and epipharynx are inserted into the skin.
At the apex of the rostrum are some tactile hairs.

The maxillæ are triangular chitinous plates situated on either side of
that portion of the head where the biting organs emerge. These
structures serve to protect the origin of the epipharynx and
mandibles, rest upon the cutaneous surface in the act of biting,
thereby steadying the head and serving as a fulcrum when the flea
withdraws its biting apparatus when through feeding. The maxillæ have
their palpi, which are four jointed, paired organs coming out at the
anterior lower angle of the head. Their function is sensory.

INSIDE THE HEAD.

The hypopharynx is a chitinous plate forming part of the floor of the
aspiratory canal. To its under surface are attached the muscles which
operate the salivary pump. Its lower portion is connected to the
mandibles, while its upper portion is connected to the posterior
portion of the floor of the aspiratory pharynx by a membranous
ligament.

The aspiratory pharynx extends from the connection of the hypopharynx
with the mandibles to the œsophageal commissure. In a general way it
first passes upward and then turns, passing backward. Its roof is
formed by the continuation of the ventral surface of the epipharynx,
while its floor is formed by the hypopharynx below and above by the
chitinous layer which is continuous with the œsophagus. The anterior
end of this particular portion curves strongly downward, where it is
attached to the upper portion of the hypopharynx by a membranous
ligament. In a general way it may be divided into a vertical and
longitudinal portion. The longitudinal portion expands laterally, so
that its capacity is greatly increased when dilated. Into the floor of
this longitudinal portion empties the vertical part of the aspiratory
pharynx, and at the junction of the two there seems to be a valvular
arrangement, preventing blood from escaping after it has entered the
upper part of the aspiratory canal. The œsophagus starts at the
œsophageal commissure and ends in the gizzard. It is not expanded as
in some insects, forming a gullet, but is practically the same
diameter throughout its entire extent. It is lined with chitin,
surrounded by a delicate basement membrane.

The gizzard is a mushroom-shaped organ, opening into the stomach and
receiving the contents of the œsophagus and the aspiratory pharynx.
From its anterior concave inner surface project a number of
finger-like processes that arise from a basement membrane. They are
lined with chitin, and each one near its base contains an elongated
nucleus. These processes reach to the center of the gizzard and in a
general way point towards the opening into the stomach. The gizzard is
surrounded by circular bands of muscle fibers. Its function is not
entirely understood. Wagner[205] has pointed out that these processes
may act as whips to defibrinate the blood. It is more probable that
their action is mainly valvular, preventing regurgitation of blood
from the stomach.

The stomach of a flea is large and is capable of great distention. It
is composed of a layer of secretory cells, resting on a basement
membrane, the organ being surrounded by muscle fibers passing in
different directions. The epithelial surface is thrown into little
projections like villi. As absorption occurs in the stomach, these
villi, or projections of the epithelial cells, may serve to increase
the absorptive surface as well as serving a glandular function. At the
anterior end of the stomach are the cecal glands.

The intestine is short, receives the excretion from the Malpighian
tubules, and ends in the rectum. In the rectum may be seen the
so-called “rectal glands.” All of the alimentary canal, with the
exception of the stomach, is lined with chitin. The stomach and the
rectum are capable of peristaltic movement.

The salivary glands, four in number, two on each side of the anterior
part of the stomach, are simple acinous glands, lined with a single
layer of secreting cells. The lumen of the glands is large and acts as
a reservoir for the salivary secretion. The ducts from these glands
unite to form a single duct which passes beneath the subœsophagal
ganglion and empties into the salivary pump. This duct is lined on its
inner surface by a spiral arrangement of chitin, giving it a very
characteristic appearance.

DESCRIPTION OF FIGURE SHOWING MOUTH PARTS.

1. Epipharynx.

2. Mandibles.

3. Rostrum, paired portion.

4. Rostrum, unpaired portion.

5. Maxilla.

6. Maxillary palpus.

7. Salivary grooves.

8. Basal element of rostrum.

9. Basal element of mandibles.

10. Salivary pump.

11. Salivary duct.

12. Vertical portion, aspiratory canal.

13. Longitudinal portion, aspiratory canal.

14. Œsophagus.

15. Œsophageal ganglia.

16. Muscles operating aspiratory canal.

17. Hypopharynx.

18. Muscles operating salivary pump.

19. Ligament connecting hypopharynx with floor of aspiratory canal.

PLATE I.

MOUTH PARTS OF CERATOPHYLLUS FASCIATUS.
]

THE ACT OF BITING.

The epipharynx, or pricker, makes an opening into the skin, through
which the mandibles are inserted. These organs, by means of their
serrations and independent movement, then enlarge the opening as with
a saw, permitting them, with the epipharynx, to pass deeper and deeper
until the points of the maxilla rest upon the cutaneous surface. The
labial palpi serve as a protective case when the organs are not in
action. When in action they serve as a guide to the piercing organs,
but are not inserted into the skin. They double up like a bow, on each
side, the bend of the bow becoming greater and greater as the biting
apparatus passes deeper and deeper. Mitzmain[206] has pointed out that
the spring-like action of this bow may assist the flea to withdraw the
mandibles and epipharynx.

During the process of penetration the salivary pump receives saliva
from the salivary glands and pumps it down, through the channel in the
mandibles, into the wound. It will be seen that the hypopharynx, being
attached above by a membranous ligament and connected intimately with
the mandibles below, moves downward with these organs as they pass
through the skin. At the same time the muscles attached to its under
surface and the salivary pump contract, enlarging the lumen of the
pump. When the mandibles are retracted the salivary pump collapses,
thereby forcing the saliva out with the movement upward of the
mandibles. At the proper time the muscles operating the aspiratory
pharynx contract, drawing the canal open and aspirating blood through
the canal made by the approximation of the epipharynx and mandibles
and into the aspiratory pharynx. When full, the muscles relax from
before backward and the pharynx, by means of the elastic reaction of
its chitinous lining, contracts and forces the blood backward through
the gizzard and into the stomach. It has already been pointed out that
the finger-like processes in the gizzard probably act as valves to
prevent regurgitation from the stomach.

HOW THE FLEA INFECTS ITS HOST.

The exact method by which the flea can transmit plague from animal to
animal has, in our opinion, never been satisfactorily explained. There
have been several explanations offered: First, that the rat may eat
the flea. Miller[207] has found that the _Hepatazoon perniciosum_ is
transmitted from rat to rat through the rat eating the mite, _Lelaps
echidninus_, which acts as the intermediate host. We know, however,
that when a rat is fed on plague material a mesenteric bubo is the
rule, while in naturally infected rats a mesenteric bubo is a rare
condition. This, then, negatives the possibility of plague being
contracted through eating the flea.

Another explanation is that the infection comes from the saliva
injected at the time of biting. We have already stated that after
repeated examinations, both by dissecting out the salivary glands and
by serial sections of the entire flea, plague bacilli have never been
demonstrated in these glands or anywhere outside of the alimentary
tract.

Another explanation has been advanced, that the bacillus is introduced
by the contaminated mandibles. It is not possible to exclude this as a
means of infection, although the Indian Plague Commission made
numerous investigations and was unable to demonstrate the bacillus on
the mandibles.

The possibility of infection taking place by regurgitation from the
stomach has also been considered. As the stomach is guarded by the
finger-like processes in the gizzard which seem to act as competent
valves, and as the movement of the blood aspirated by reason of the
mechanism already explained is in a backward direction, it would seem
improbable that there is any regurgitation from the stomach.

The most plausible explanation that has been advanced has been based
on an observation that blood-sucking insects at the time of biting
frequently eject a drop of blood from the rectum. We know that the
rectum may contain numerous plague bacilli, and it is supposed that
this blood ejected in the vicinity of the bite is either brought in
contact with the slight wound by the feet or mandibles of the flea
itself or is rubbed in as a result of scratching. Verjbitski has shown
that an emulsion of the feces of fleas or any plague material when
placed upon the bitten part before the expiration of twenty-four hours
is sufficient to give the animal plague. After twenty-four hours the
animals did not develop plague, it being supposed that the slight
wound in the skin made by the biting apparatus had healed. It is
probable that this ejection of blood is purely accidental and does not
necessarily occur at the time of biting, but it is likely that the
insect had just previously had a full meal, which had been digested
and passed into the rectum. In the many biting experiments done by
McCoy and Mitzmain they report never having seen this ejection of
rectal contents taking place. It might also be stated that where they
used plague-infected fleas none of the animals developed plague after
being bitten.

ENUMERATION OF FLEAS THAT HAVE BEEN FOUND ON RATS.

Various writers have reported the following fleas taken off rats:

Family SARCOPSYLLIDÆ Taschenberg.

Genus DERMATOPHILUS.

1. _Dermatophilus cæcata_ Enderlein.—Seventeen specimens (females)
were found by Doctor Enderlein on the skin behind the ears of a
specimen of _Mus rattus_ from Saopaulo, Brazil.

Genus ECHIDNOPHAGA Olliff.

2. _Echidnophaga gallinacea_ Westwood.—Tiraboschi has found this flea
on the _Mus rattus_ in Italy.

3. _Echidnophaga rhynchopsylla_ Tiraboschi.—This flea has been taken
in Italy from _Mus rattus_ and _Mus alexandrinus_. It has been
described by Rothschild under the name of _Echidnophaga murina_.

Family PULICIDÆ Taschenberg.

Genus CERATOPHYLLUS Curtis.

4. _Ceratophyllus fasciatus_ Bosc.—This is the common rat flea of
Europe and the United States. It has also been found in Cape Town,
Australia, and is occasionally found on rats in India.