Chapter XII: Appendix: “Rhizopods in Poliomyelitis acuta.” (6)

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The appearance of quartana duplex or triplex is conditional on the presence in the blood of the patient of two or three groups of _Plasmodia_ differing in their development by twenty-four hours.

The chief distinctive characters of the quartan parasite are: (1) The erythrocyte is unchanged in size; (2) the rings are compact and show pigment early; in the larger forms the chromatin is dense and relatively plentiful; (3) the pigment, which is relatively well-marked, may be arranged at the periphery.

*Laverania malariæ*, Grassi and Feletti, 1890 = *Plasmodium falciparum*, Welch, 1897.

Syn.: _Plasmodium malariæ_ var. _quotidianæ_, Celli et Sanf., 1891;
_Hæmamœba malariæ præcox_, Gr. et Fel., 1892 (nec _H. præcox_,
Gr. et Fel., 1890); _Hæmamœba laverani_, Labbé, 1894; _Hæmatozoön
falciparum_, Welch, 1897; _Hæmosporidium undecimanæ_ and _H.
sedecimanæ_ and _H. vigesimo-tertianæ_, Lewkowitz, 1897; _Hæmamœba
malariæ parva_, Lav., 1900; _Plasmodium præcox_, Dofl., 1901;
_Plasmodium immaculatum_, Schaud., 1902; _Plasmodium falciparum_,
Blanch., 1905.

The names most commonly used for the parasite of malignant tertian malaria are _Plasmodium falciparum_ and _Laverania malariæ_.

The summer and autumn fever (_febris æstivo-autumnalis_), also called malignant tertian or sub-tertian, is caused by a malarial parasite which is distinguished by the small size of its schizont, while the gametocytes are crescentic (figs. 81, 88).

Most authors identify this kind of fever or the parasites which
cause it (_Laverania malariæ_) with the pernicious malaria of the
tropics. Ziemann, however, repeatedly has drawn attention to certain
small but definite differences between the usual malignant tertian
or pernicious parasites which occur in the tropics and the tropical
parasites of some malarial districts, particularly of West Africa,
and insists that at least two varieties or sub-species occur. Other
investigators distinguish from this or these forms a quotidian
parasite. On the other hand, the assertion is made that there are no
specific differences, but that the malignant or pernicious tertian
parasite which normally needs forty-eight hours for its development
in the blood of man, can also develop in twenty-four hours. The
establishment of the duration of the development is a matter of
especial difficulty, because the stages of schizogony are far less
numerous in the peripheral blood than in that of the internal
organs. It is also stated that the tropical parasite very seldom
forms crescentic but rather rounded gametocytes. According to such
an observation the organism would belong to _Plasmodium_ and not to
_Laverania_. The question whether the tropical fevers are caused by
two different parasites does not seem to be definitely settled.

The young trophozoite of the malignant, pernicious tertian, or sub-tertian parasite (fig. 87) are but slightly active and are very small, even after the formation of the comparatively large food vacuole, which makes the body appear annular (“signet ring” stage). Often two and even more parasites are found in one blood corpuscle.

Fully grown they only attain two-thirds or less of the diameter of the erythrocytes, which display an inclination to shrink and then appear darker than the normal (brass-coloured). In the early stage dots or stippling--sometimes called Maurer’s dots--appear on the blood corpuscles as in those attacked by the ordinary tertian parasite (_Plasmodium vivax_), but the Maurer’s dots are relatively coarse and few, and are not easily stained. These dots were first described by Stephens and Christophers in 1900, and subsequently by Maurer in 1902.

About thirty hours after the entrance into the blood corpuscles, the parasites are rarely found in the peripheral blood, but they are present in the internal organs, and especially in the spleen. The schizogony, which now begins in the internal organs, proceeds on the same lines as that of the quartan parasite, that is, usually with the merozoites radially arranged around a central agglomeration of dark brown pigment.

The number of merozoites formed is quoted differently, _e.g._, 8 to 24, on an average 12 to 16. However, according to the recent cultural researches of J. G. and D. Thomson[204] (1913) the number of merozoites of _P. falciparum_ is 32. D. Thomson, from examination of spleen smears at autopsy, also concludes that the number of merozoites may reach 32. During their formation the blood corpuscle which is attacked gets paler and disintegrates.

[204] _Proc. Roy. Soc._, B, lxxxvii, p. 77.

The gametocytes which finally appear are attenuated, curved bodies, rounded at each end and known as crescents (figs. 81, 88), and are provided with a nucleus and with coarse pigment masses. In the males the pigment is more scattered than in the females, where it is around the nucleus. Their length is 9 µ to 14 µ, and their breadth is 2 µ to 3 µ. At first they are still in the pale blood corpuscles, later they free themselves and are found in numbers in the peripheral blood in cases of pernicious malaria of Southern Europe and the tropics, while, on the other hand, they occur much more rarely in the peripheral blood in West African malignant tertian. Their further development takes place under the same conditions as in the other malarial parasites.

D. Thomson (1914),[205] from studies of autopsy smears, has shown that crescents develop chiefly in the bone-marrow and spleen, and take about ten days to grow into the adult state in the internal organs. He believes that crescents are produced from ordinary asexual spores. Quinine, he states, has no direct destructive action on crescents, but it destroys the asexual source of supply.

[205] _Annals Trop. Med. and Parasitol._, viii, p. 85.

The sporozoites of _Laverania malariæ_ (_P. falciparum_) are represented in fig. 89.

The principal distinctive characters of the malignant tertian parasite are: (1) The ring forms are very small, occasionally bacilliform, and may be marginal (“accolé” of Laveran); (2) the larger trophozoites are often ovoid, and about one-third or one-half of the erythrocyte in size; (3) the infected red cells sometimes show coarse stippling (Maurer’s dots); (4) the gametocytes, or sexual forms, are crescentic in shape.

J. W. W. Stephens (1914) has described a new malarial parasite of man; it is called _Plasmodium tenue_. It is very amœboid, with scanty cytoplasm and much chromatin, sometimes rod-like or irregular. The parasite was described from a blood-smear of an Indian child. The creation of a new species for this parasite has been criticized by Balfour and Wenyon, and by Craig.

*Plasmodium relictum*, Sergent, 1907.

Syn.: _Plasmodium præcox_, Grassi and Feletti, 1890; _Plasmodium
danilewskyi_, Gr. et Fel., 1890; _Hæmamœba relicta_, Gr. et Fel.,
1891; _Proteosoma grassii_, Labbé, 1894.

Hæmamœboid, pigment-producing, malarial parasites are often found in
birds. Like the human malarial parasites they have been variously
named. Labbé created the genus _Proteosoma_ for them, and this name
is still often used as a distinctive one unofficially. The correct
name is stated to be either _Plasmodium relictum_ or _P. præcox_,
or possibly even _P. danilewskyi_, assuming that there is only one
species. The nomenclature of the malarial parasites is most confused.
The avian malarial parasites are transmitted by Culicine mosquitoes.

The organism was discovered by Grassi in the blood of birds in Italy,
and causes a fatal disease in partridges in Hungary. Sparrows are
affected in India, and it was this Plasmodium in which Ross first
traced the development of a malarial parasite in a mosquito. The
parasite may be transmitted from bird to bird by blood-inoculation,
canaries being very susceptible.

The principal stages of the avian plasmodium closely resemble those
of the malarial parasites of man. In its earliest stage _P. relictum_
is unpigmented, but soon the trophozoite grows and becomes pigmented,
meanwhile displacing the nucleus of the avian red-blood corpuscle,
a characteristic feature, distinguishing it from _Halteridium_.
Schizonts are formed, each of which gives rise to about nine
merozoites in the circulating blood. Sexual forms or gametocytes also
occur in the blood. These develop in _Culex fatigans_, _C. pipiens_
and _C. nemorosus_. Oökinetes or vermicules are formed in twelve
to fifteen hours in the stomach of the mosquito, and in one to two
days well-developed round oöcysts may be seen. In three to four days
sporoblasts have formed within the oöcysts and young sporozoites
begin to develop. In nine to ten days the oöcysts are mature, being
filled with sporozoites. The oöcysts then burst and the sporozoites
travel through the thoracic muscles to the salivary glands of the
Culicine.

Neumann, experimenting with canaries, found that _Stegomyia fasciata_
could transmit the infection, but less efficiently than species of
_Culex_.

THE CULTIVATION OF MALARIAL PARASITES.

The successful cultivation of malarial parasites _in vitro_ was first recorded by C. C. Bass and by Bass and Johns (1912).[206] Since then, J. G. and D. Thomson,[207] and McLellan (1912–13), Ziemann[208] and others have repeated the experiments.

[206] _Journ. Exptl. Med._, xvi, p. 567.

[207] _Annals Trop. Med. and Parasitol._, vi, p. 449; vii, pp. 153, 509.

[208] _Trans. Soc. Trop. Med. and Hyg._, vi, p. 220.

DIFFERENTIAL CHARACTERS OF THE HUMAN MALARIAL PARASITES.

Essentially the method of cultivation, as used by Thomson, is as follows: 10 c.c. of infected blood are drawn from a vein and transferred to a sterile test tube, in which is a thick wire leading to the bottom of the tube. One-tenth of a cubic centimetre of a 50 per cent. aqueous solution of glucose or dextrose is placed in the test tube, preferably before adding the blood. The blood is defibrinated by stirring gently with the wire. When defibrination is complete the wire and the clot are removed, and the glucose-blood is transferred, in portions, to several smaller sterile tubes, each containing a column of blood about one inch in height. The tubes are plugged and capped and then transferred, standing upright, to an incubator kept at a temperature of 37° C. to 41° C. The blood corpuscles soon settle, leaving a column of serum at the top, to the extent of about half an inch in each tube. The leucocytes need not be removed by centrifugalization. J. G. Thomson (1913) and his collaborators did not find it necessary to destroy the complement in the serum, and they found that the malarial parasites developed at all levels in the column of corpuscles, and not merely on the surface layer of the corpuscles as first stated by Bass and Johns.

So far only the asexual generation of the malarial parasites has been grown _in vitro_. Thomson rarely observed hæmolysis in the cultures. Clumping of the malignant tertian parasites occurred. In cultures of the benign tertian parasite (_Plasmodium vivax_) clumping was not observed. J. G. and D. Thomson consider that this difference as regards clumping explains why only young forms of malignant tertian are found in peripheral blood, as the clumping tendency of the larger forms causes them to be arrested in the finer capillaries of the internal organs. It also explains the tendency to pernicious symptoms, such as coma, in malignant tertian malaria. Further it was found from cultures that _P. falciparum_ was capable of producing thirty-two spores (merozoites) in maximum segmentation, while _P. vivax_ produced sixteen spores (merozoites) as a rule, though the number might be greater than sixteen. (Quartan parasites produce eight spores or merozoites in schizogony.)

It may also be mentioned here that _Babesia_ (_Piroplasma_) _canis_ has been successfully cultivated _in vitro_ by Bass’s method. This has been accomplished by Thomson and Fantham,[209] Ziemann, and Toyoda in 1913. J. G. Thomson and Fantham used the simplified Bass technique recorded above, namely, infected blood and glucose, incubating at 37° C. In one of the _B. canis_ cultures, starting with heart blood of a dog containing corpuscles infected with one, two, or, exceptionally, four piroplasmata, Thomson and Fantham succeeded in obtaining a maximum of thirty-two merozoites in a corpuscle. The cultures are infective to dogs and sub-cultures have been obtained.

[209] _Annals Trop. Med. and Parasitol._, vii, p. 621.

Family. *Piroplasmidæ*, França.

The parasites included in this provisional family or group belong to the Hæmosporidia. They are minute organisms, sometimes amœboid, but usually possessing a definite form. They are endoglobular, being contained within mammalian red blood corpuscles, but they produce no pigment. The true Piroplasmata, belonging to the genus _Babesia_, destroy the host corpuscles, setting free the hæmoglobin, which is excreted by the kidneys of the cow, sheep, horse, dog, etc., acting as host. The disease produced, variously called piroplasmosis or babesiasis, is consequently characterized by a red coloration of the urine known as hæmoglobinuria, or popularly as “red-water.” One of the best known piroplasms is _Piroplasma bigeminum_ or _Babesia bovis_ (probably the latter name is correct), which is the causal agent of “Texas fever” or “red-water” in cattle and is spread by ticks.

Of recent years, researches on the morphology of these blood parasites has led to their separation into various genera and species. However, our knowledge is still very far from complete. The various genera recognized by França[210] (1909), and placed in a provisional family, Piroplasmidæ, may be listed, though further research may lead to emendations:--

[210] _Arch. Inst. Bact. Camara Pestana_, iii, p. 11.

(1) _Babesia_ (Starcovici) or _Piroplasma_ (Patton). Pyriform parasites, dividing by a special form of budding or gemmation with chromatin forking, as well as by direct binary fission. Parasitic in oxen, dogs, sheep, horses, etc.

(2) _Theileria_ (Bettencourt, França and Borges). Rod-shaped and oval parasites occurring in cattle and deer. _T. parva_ is the pathogenic agent of African East Coast fever in cattle.

(3) _Nuttallia_ (França). Oval or pear-shaped parasites, with multiplication in the form of a cross. _N. equi_[211] (fig. 90) of equine “piroplasmosis” (nuttalliosis). _N. herpestidis_ in a mongoose.

[211] _Parasitology_, v (1912), p. 65.

(4) _Nicollia_ (Nuttall). Oval or pear-shaped parasites with characteristic nuclear dimorphism, and with quadruple division at first fan-like, then like a four-leaved clover. _N. quadrigemina_ from the gondi.

(5) _Smithia_ (França). Pear-shaped, single forms stretching across the blood corpuscle. Multiplication into four in the form of a cross. _S. microti_ from _Microtus arvalis_, _S. talpæ_ from the mole.

(6) _Rossiella_ (Nuttall). This belongs to the family Piroplasmidæ of França. It is intracorpuscular and non-pigment forming, occurring singly, in pairs, or occasionally in fours. It is usually round and larger than Babesia. The parasite multiplies by binary fission. _R. rossi_ in the jackal.

The genus _Babesia_ is the best known and most important, and will be considered next.

Genus. *Babesia*, Starcovici, 1893.

Syn.: _Pyrosoma_, Smith and Kilborne, 1893; _Apiosoma_, Wandolleck,
1895; _Piroplasma_, W. H. Patton, 1895; _Amœbosporidium_, Bonome,
1895.

The organisms belonging to this genus are pyriform, round or amœboid. The characteristic mode of division is as follows: Just before division the parasite becomes amœboid and irregular in shape, (fig. 91, _1–5_) with a compact nucleus. The latter gives off a nuclear bud. This nuclear bud divides into two by forking (fig. 91, _6_, _7_). The chromatin forks grow towards the surface of the body of the rounded parasite, and then two cytoplasmic buds grow out. The forking nuclear buds, which are *Y*-shaped, pass into the cytoplasmic outgrowths[212] (fig. 91, _8_, _9_). The buds gradually increase in size at the expense of the parent form until they become two pear-shaped parasites joined at their pointed ends. The connecting strand shrinks and the two daughter forms separate (fig. 91, _10–14_). The pyriform parasites after having exhausted the blood corpuscle escape from it (fig. 91, _15_), and seek out fresh host corpuscles, entering by the rounded, blunt end (fig. 91, _1_). It is the pyriform phase of the parasite which penetrates red blood corpuscles, not rounded forms, which die if set free. The pyriform parasite, however, becomes rounded (fig. 91, _2_, _3_), soon after its entry into a fresh host cell. This interesting mode of division by gemmation and chromatin forking has been made diagnostic of the genus _Babesia_ by Nuttall.[213] Rounded forms of _Babesia_ divide by binary fission, and this direct method can also be adopted by the other forms of Babesia.

[212] Nuttall and Graham-Smith, _Journ. Hyg._, vii, p. 232.

[213] “Piroplasmosis,” Herter Lectures, _Parasitology_, vi, p. 302.

The distribution of the chromatin in the pear-shaped _Babesia_,
as seen in _B. canis_ and _B. bovis_, is interesting. The main
nuclear body consists of a karyosome surrounded by a clear area.
There is also a loose (chromidial) mass of chromatin representing
the remains of the chromatin forks seen during the formation of the
parasite as a daughter form by gemmation. Occasionally there is
a small dot or point, the so-called “blepharoplast” of Schaudinn
and Lühe. This minute dot is not a flagellate blepharoplast, for
there is no flagellate stage in the life-history of Babesia. These
nuclear phenomena have been described by Nuttall and Graham-Smith
and Christophers (1907)[214] for _B. canis_, by Fantham (1907)[215]
for _B. bovis_, and by Thomson and Fantham (1913) from glucose-blood
cultures of _B. canis_.

[214] _Sci. Mems. Govt. India_, No. 29.

[215] _Quart. Journ. Microsc. Sci._, li, p. 297.

Babesia are tick borne, as was first shown by Smith and Kilborne (1893). The developmental cycle in the tick is incompletely known. The best accounts are those of Christophers (1907)[216] for _B. canis_ and Koch (1906) for _B. bovis_, and these accounts are supplementary. The principal stages, so far as known, may be summarized thus:--

[216] _Sci. Mems. Govt. India_, No. 29.

(1) The piroplasms taken by the tick in feeding on blood pass into
the tick’s stomach. The pyriform parasites, which alone are capable
of further development, are set free from the blood corpuscles. In
about twelve to eighteen hours they become amœboid, sending out long,
stiff, slender, pointed pseudopodia. The nucleus of each parasite
divides unequally into two. Similar forms have been obtained in
cultures. These stellate forms may be gametes, and according to Koch
fuse in pairs.

(2) A spherical stage follows, possibly representing the zygote. This
grows, and a uninucleate globular mass results. This form is found in
large numbers on the third day, according to the observations of Koch.

(3) A club-shaped organism is next formed. This may represent an
oökinete stage. The club-shaped bodies are motile and gregarine-like,
and are about four times the size of the blood forms. These
club-shaped bodies and subsequent stages were described by
Christophers in the development of _B. canis_ in the dog-tick,
_Rhipicephalus sanguineus_.

(4) The club-shaped bodies pass from the gut of the tick into the
ovary, and so get into the ova. There they become globular, and later
are found in the cells of the developing tick-embryo. The parasites
are, then, transmitted hereditarily. Similar globular bodies are
found in the tissue cells of the body of tick nymphs which have
taken up piroplasms. The globular stage was called the “zygote” by
Christophers, but it may correspond to the oöcyst of Plasmodia.

(5) The globular body divides into a number of “sporoblasts,” which
become scattered through the tissues of the larval or nymphal tick,
as the case may be.

(6) The sporoblasts themselves divide into a large number of
sporozoites, which are small uninucleate bodies, somewhat resembling
blood piroplasms. The sporozoites collect in the salivary glands of
the tick. They are inoculated into the vertebrate when the tick next
feeds.

The chief species of _Babesia_ and their pathogenic importance may be listed thus:--

(1) _Babesia bovis_ (Babes) produces infectious hæmoglobinuria of cattle in Europe and North Africa. It is transmitted by _Ixodes ricinus_. A similar parasite also occurs in deer.

(2) _Babesia bigemina_ (Smith and Kilborne) produces Texas fever, tristeza, or red-water in cattle in North and South America, South Africa and Australia. It is transmitted by _Boöphilus annulatus_ in North America, by _B. australis_ in Australia, South America, and the Philippines, and by _B. decoloratus_ in South Africa.

The parasite is from 2 µ to 4 µ long, and from 1·5 µ to 2 µ broad.

_Babesia bigemina_ may be the same parasite as _B. bovis_.

(3) _Babesia divergens_ (MacFadyean and Stockman) is a small parasite. It is found in cattle suffering from red-water in Norway, Germany, Russia, Hungary, Ireland, Finland, and France, and is transmitted by _Ixodes ricinus_.

(4) _Babesia canis_ (Piana and Galli-Valerio) gives rise to malignant jaundice or infectious icterus in dogs in Southern Europe, India, and other parts of Asia and North Africa, where it is transmitted by _Rhipicephalus sanguineus_. In Africa generally, especially South Africa, the disease is transmitted by _Hæmaphysalis leachi_. _Babesia canis_ varies from 0·7 µ to 5 µ, the size depending partly on the number of parasites within the corpuscle. It averages about 3 µ. It has been cultivated in Bass’ medium (glucose and infected blood), see p. 172.

In India _Piroplasma gibsoni_ (Patton) infects hunt dogs and jackals. It is annular or oval in shape.

(5) _Babesia ovis_ (Babes) produces “Carceag,” a disease of sheep in Roumania, the Balkan Peninsula, Italy, and Transcaucasia. It varies in size from 1 µ to 3 µ. It is transmitted by _Rhipicephalus bursa_. The parasite has recently been recorded from Rhodesia.

(6) _Babesia caballi_ (Nuttall and Strickland) causes “biliary fever” in equines. The parasite occurs in Russia, Roumania, and Transcaucasia. It varies in size from 1 µ to 2 µ. It is transmitted by _Dermacentor reticulatus_.

It should be mentioned that _Nuttallia equi_ also causes
“piroplasmosis” in equines, with symptoms of hæmoglobinuria and
jaundice in Italy, Sardinia, many parts of Africa, Transcaucasia,
India, and Brazil. In Africa it is transmitted by _Rhipicephalus
evertsi_. It has been shown experimentally that a horse recovered
from _Babesia caballi_ was susceptible to the inoculation of
_Nuttallia equi_ blood.

(7) _Babesia pitheci_ (P. H. Ross) was found in a monkey, _Cercopithecus_ sp., in Uganda. The pear-shaped forms measure 1·5 µ by 2·5 µ.

(8) _Babesia muris_ (Fantham)[217] was found in white rats. The pyriform parasites are 2 µ to 3 µ long and 1 µ to 1·5 µ broad; oval forms are 0·5 to 1·5 µ diameter.

[217] _Quart. Journ. Microsc. Sci._, 1, p. 493.

The usual symptoms of babesiasis (piroplasmosis) are high fever, loss of appetite, hæmoglobinuria, icterus, anæmia, paralysis, and death in about a week in acute cases. In chronic cases there is anæmia, and hæmoglobinuria is less marked. When animals recover, there are still some piroplasms left in the blood. “Recovered” or “salted” animals are not susceptible to reinfection, but ticks feeding on them acquire piroplasms, and are a source of danger to freshly imported animals.

_Treatment._--Trypan-blue is the best drug, as shown by Nuttall
and Hadwen[218] (1909). It should be administered intravenously
in 1 to 1·5 per cent. aqueous solution. A dose of 5 to 10 c.c. is
curative for dogs, one of 100 to 150 c.c. for horses and cattle.
Unfortunately, the tissues are coloured blue by the drug. The
“salted” animals, after trypan-blue treatment, still harbour the
parasites in their blood for years.

[218] _Parasitology_, ii, p. 156.

Genus. *Theileria*, Bettencourt, França and Borges, 1907.

The organisms belonging to this genus are rod-like or bacilliform,
and coccoid or round.

The best known of the species of Theileria is _T. parva_, the
pathogenic agent of East Coast fever or Rhodesian fever in cattle in
Africa.

*Theileria parva*, Theiler, 1903.

Syn.: _Piroplasma parvum_.

In the blood corpuscles of infected cattle minute rod-like and oval parasites are seen. Some are comma shaped and others are clubbed (fig. 92, _1–12_). The rod-like forms measure 1 µ to 3 µ in length by 0·5 µ in breadth; the oval forms are 0·7 µ to 1·5 µ in diameter. The intracorpuscular parasites are said by R. Gonder (1910) to be gametocytes, the rod-like forms being thought to be males, the oval forms to be females. Free parasites are practically never seen in the blood. It is known that it is impossible to produce the disease in a healthy animal by blood inoculation, but only by intraperitoneal transplantation of large pieces of infected spleen (Meyer). There may be as many as eight parasites in a corpuscle. The chromatin is usually at one end of the organism. In some parasites the appearance of the chromatin suggests division, but such division, if it takes place, must be very slow, as it has not been actually seen in progress. The red blood corpuscles appear merely to act as vehicles for the parasites (Nuttall, Fantham, and Porter).[219]

[219] _Parasitology_, ii, p. 325; iii, p. 117.

In the internal organs, especially the lymphatic glands, spleen
and bone-marrow, are found multinucleate bodies known as Koch’s
blue bodies (fig. 92, _13–18_). These are schizonts, according
to Gonder.[220] The actual Koch’s blue bodies are said to be
extracellular, but similar multinucleate bodies, schizonts, occur
in lymphocytes. The schizonts divide and the merozoites resulting
probably invade the red blood corpuscles in the internal organs.
Gonder considers that the sporozoites injected by the tick collect in
the spleen and lymphatic glands, penetrate the lymphocytes and give
rise to the schizonts.

[220] _Zeitschr. f. Infekt. paras. Krankh. u. Hyg. d. Haustiere_, viii, p. 406.

Gonder has studied the cycle of _T. parva_ in the tick. He states
that the gametocytes leave the host corpuscles and give rise to
gametes, then conjugation occurs producing zygotes. The zygotes
are then said to become active to form ookinetes, and to enter the
salivary glands of the tick. Multiplication is said to occur therein,
producing a swarm of sporozoites. This work needs confirmation.

_T. parva_ is transmitted by _Rhipicephalus appendiculatus_, _R.
simus_, _R. evertsi_, _R. nitens_, and _R. capensis_. The parasites
are not hereditarily transmitted in _Rhipicephalus_, but when taken
by the transmitter at one stage of its development the tick is
infective in its next stage (_e.g._, if the larva becomes infected,
then the nymph is infective; if the nymph becomes infected, then the
adult is infective).

An animal recovered from _Theileria parva_ is incapable of infecting
ticks, but few animals recover from East Coast fever. Animals
suffering therefrom do not show hæmoglobinuria.

*Theileria mutans*, Theiler, 1907·

Syn.: _Piroplasma mutans_.

This is transmissible experimentally by blood inoculation. It
occurs in cattle in South Africa and Madagascar and is apparently
non-pathogenic. No Koch’s blue bodies are formed. It is transmitted
by ticks.

_Theileria annulata_ (Dschunkowsky and Luhs) occurs in cattle in
Transcaucasia.

A Theileria (_T. stordii_) has been found in a gazelle (França, 1912).

Genus. *Anaplasma*, Theiler, 1910.

This genus[221] may be mentioned here. The organisms included therein
are, according to Theiler, coccus-like, consisting of chromatin,
and are devoid of cytoplasm. They occur in the red blood corpuscles
of cattle, causing a disease characterized by destruction of red
cells, fever and anæmia, but with yellow urine. The disease is
tick transmitted. The bodies now called _Anaplasma marginale_ were
formerly described as marginal points. They multiply by simple
fission. They are said by Theiler to cause gall-sickness in cattle in
South Africa. Some authors doubt whether these bodies are organismal.

[221] _Bull. Soc. Path. Exot._, iii, p. 135.

Genus. *Paraplasma*, Seidelin, 1911.

Under this generic name Seidelin described certain bodies found by him in cases of yellow fever in 1909. The type species is _P. flavigenum_,[222] and is claimed by Seidelin to be the causal agent of yellow fever.

[222] _Yellow Fever Bulletin_, i, p. 251.

_Paraplasma flavigenum_ occurs in the early days of the disease as small chromatin granules with or without a faint trace of cytoplasm. The bodies are usually intracorpuscular. Also, somewhat larger forms, with distinct cytoplasm, are seen in small numbers. During the later days of the disease still larger forms are found, and these occur also in sections of organs (_e.g._, kidney) made post-mortem. Some of these larger forms are perhaps schizonts. In the second period of the disease possible micro- and macro-gametes may be found, some of which are extracorpuscular. Some small free bodies have been seen. Recently schizogony has been stated to occur in the lungs, and it is said that guinea-pigs can be inoculated with _Paraplasma flavigenum_, and show yellow pigment in the spleen.

Seidelin places _Paraplasma_ in the _Babesiidæ_, with resemblances more particularly to _Theileria_. V. Schilling-Torgau and Agramonte have criticized these findings; the former considers them to be the resultant of certain blood conditions.

_P. subflavigenum_ was found by Seidelin in 1912 in a man suffering from an unclassified fever in Mexico.

Further, it is now known that a Paraplasma occurs naturally in guinea-pigs. More researches are needed on these matters, as some writers (_e.g._, Wenyon and Low) claim that the bodies are not organismal.

-------------------------------------------------------------------- |_Paraplasma flavigenum._--The Yellow Fever Commission (West Africa) | |in their third report, dated 1915, have come to the conclusion that | |there is no evidence that the bodies termed _Paraplasma flavigenum_ | |are of protozoal nature or that they are the causal agents of yellow| |fever. | --------------------------------------------------------------------

Sub-class. NEOSPORIDIA, Schaudinn.

Sporozoa in which growth and spore formation usually go on together.

Order. *Myxosporidia*, Bütschli.

These parasites, which were discovered by Johannes Müller (1841),
live principally in fishes, and occasionally cause destructive
epizoötics amongst their hosts. Müller first observed them in
the form of whitish-yellow pustules on the skin or on the gills
of various fishes. These pustules contained masses of small
shell-covered bodies with or without tails (“psorosperms,” see
fig. 93). Similar bodies were also found in the air bladders of
certain fish. Creplin (1842) demonstrated the resemblance of the
cysts (“psorosperm tubes”) harbouring the psorosperms to the
“pseudonavicella-cysts” of a gregarine, as described by v. Siebold.
Dujardin (1845) considered that there was possibly some connection
between the protoplasmic “psorosperm tubes” and the spores they
contained, and the developmental stages of monocystid gregarines
from the vesiculæ seminales of earth-worms. The relationship of the
“fish psorosperms” was placed on a firmer basis by Leydig (1851)
and Lieberkühn. The former found numerous forms in marine fish, and
he discovered in species which live free in the gall bladder of
cartilaginous fishes that the psorosperms originated in a manner
similar to the gregarines. Lieberkühn (1854) studied the Myxosporidia
in the bladder of the pike (fig. 93, _a_, _b_, _d_), and observed
their amœboid movements, as well as the formation of the spores,
from each of which a small amœboid body escaped, a discovery that
was confirmed by Balbiani. The same author also found that spiral
filaments were enclosed in the so-called polar body, _i.e._, the
polar capsule of the psorosperm spores, and that these could be
protruded (fig. 93, _d_, and fig. 95).

The term Myxosporidia, which at the present day is universally
applied to the “psorosperm tubes,” was introduced by Bütschli
in 1881, who studied not only the structure and development of
the spores, but also the protoplasmic body of the parasites
(fig. 96), and confirmed the occurrence of numerous nuclei. Many
authors have made important additions to our knowledge of the
Myxosporidia: Perugia, Thélohan, Mingazzini, L. Pfeiffer, L. Cohn,
Doflein, Mercier, Schröder and Auerbach; while the presence of this
parasite outside the class of fishes has become known through Lutz,
Laveran, and others. The species causing disease in fishes have been
described by Ludwig, Railliet, Weltner, L. Pfeiffer, Zschokke, Hofer,
Doflein, Gurley, Plehn, Schuberg, Fantham and Porter. With regard to
classification the works of Thélohan (1895) and Gurley (1894) may be
mentioned.

The Myxosporidia live either free on the epithelial surface of hollow
organs (gall or urinary bladder, renal tubules, but never in the
intestine), or are enclosed in the tissues of their host. The gills
and muscular system are their favourite habitat, but other tissues or
organs may be attacked. Species of Myxosporidia are also known from
Amphibia, Reptilia, and a few invertebrates.

The free forms, which are often amœboid (fig. 96), move by the
aid of variously shaped pseudopodia, have a constant form, or may
exhibit contractions of the body. The tissue parasites often reach
a considerable size, so that the integument of the host forms
protuberances over them. They are of a roundish or irregular shape.
Frequently they are enveloped in a connective tissue covering formed
by the host.

The protoplasmic body in the trophic phase (fig. 96) shows a distinct
ectoplasm which is finely granular or sometimes striated, and an
endoplasm which is coarsely granular and contains many nuclei as
well as cell inclusions, such as crystals, pigment grains and fat
globules. The nuclei originate by division from the primitive nucleus
of the amœboid germ that issues from the spore. This amœbula may
or may not live intra-cellularly during the early stages of its
existence.

The multinucleate trophozoite of a Myxosporidian forms spores in
its endoplasm practically throughout its whole period of growth
(fig. 96). Vegetative reproduction by a process of external budding
or plasmotomy may also occur, as in _Myxidium lieberkühni_ from the
urinary bladder of the pike.

The myxosporidian trophozoite may produce two spores within
itself, when it is placed in the sub-order _Disporea_, or it may
produce numerous spores, which is characteristic of the sub-order,
_Polysporea_. The phenomenon of spore formation is not simple
(fig. 97), and the spore itself is surrounded by a bivalved shell or
sporocyst and contains polar capsules in addition to the amœboid germ
(fig. 97, G, H). The valves of the sporocyst and the polar capsules
are really differentiated nucleate cells, so that each spore is an
aggregate of cells rather than one cell, though only a single amœbula
issues from a spore. The accounts of spore formation vary somewhat
according to the different workers.

Spore formation is usually very complicated and there are differences
of opinion as to the interpretation of various stages, particularly
as to whether conjugation occurs therein. The process is initiated
by the concentration of cytoplasm around one of the nuclei of the
endoplasm, so that a small spherical mass or initial corpuscle is
produced, the pansporoblast (Gurley) or primitive sphere (Thélohan).
Some authors state that a pansporoblast really results from a
conjugation of two initial corpuscles (fig. 97, A-D). Nuclear
multiplication occurs within the pansporoblast (fig. 97, E), and
sooner or later two multinucleate sporoblasts are formed within it
(fig. 97, F). Each sporoblast gives rise to a single spore, which
consists of a sporocyst or envelope composed of two valves each
secreted by a cell, two polar capsules each secreted by a cell, and
the sporoplasm or amœbula which becomes binucleate (fig. 97, G).
During the process of spore formation (fig. 97) various vegetative
and reduction nuclei may be produced, in addition to those which are
essentially involved in spore formation, and the sporocyst cells may
be developed early.

Each spore contains two (figs. 94, 95) or more polar capsules which
are clearly visible in the fresh condition. Each polar capsule is
a hollow, more or less pear-shaped body, secreted by a cell and
having a well defined contour. Within it, a long, delicate, elastic
filament, the polar filament, is formed, and lies spirally coiled
in the polar capsule until just before the emergence of the amœbula
from the spore (fig. 95). The polar filament is ejected, probably
under the influence of the digestive juice, when the spore reaches
a new host, and serves to anchor the spore to the tissue with which
it is in contact, and thus allow of the emergence of the amœbula in
a situation suitable for its development. The polar capsule with its
contained polar filament has been compared with the stinging cells or
nematocysts of the Cœlentera, but it has a totally different function.

The spores fulfil the purpose of effecting transmission to other
hosts. Infection occurs by the ingestion of the parasites per os
after their escape by some means from their host. Thélohan and
others have demonstrated that the valves of the spores soon open
under the influence of the digestive juices, thus allowing the young
myxosporidia to escape. Their further history is unknown; but it may
be surmised that they either travel direct to the organs usually
affected (gall bladder, urinary bladder), or are distributed in the
body by means of the circulatory or lymphatic systems.

The Myxosporidia that invade tissues are often deadly to their
hosts. They may be present in a state of “diffuse infiltration”
when practically every organ of the body may be infected, as in
barbel disease (due to _Myxobolus pfeifferi_). On the other hand,
the parasites may be concentrated at one spot, when cysts, either
large or small, are produced. Such cysts occur on the gills of many
fishes. A few additional important pathogenic forms are _Myxobolus
cyprini_, the excitant of “pockenkrankheit” of carp, and _Lentospora
cerebralis_, parasitic in the skeleton of Salmonidæ and Gadidæ.
The skeletons of the tail, fins and skull particularly are seats
of infection, and from the skull the Lentospora can spread to the
semicircular canals, resulting in loss of power to maintain its
balance on the part of the fish. On this account the malady is
termed “drehkrankheit.” Young fish are more particularly infected.
_Myxobolus neurobius_ infects the spinal cord and nerves of trout.

Myxosporidia are divided into two sub-orders--_Disporea_ and
_Polysporea_--according to whether they form only two or several
spores during their growth. The former include two genera limited to
fishes, which are easily distinguishable by the shape of the spores:
_Leptotheca_, Thél., with a rounded spore, and _Ceratomyxa_, Thél.,
with a very elongate spore. The larger number of genera belong to the
_Polysporea_, which are divided into three families:

(1) Amœboid germ with a vacuole {(a) With two polar capsules.--
the contents of which do { _Myxidiidæ._
not stain with iodine. {(b) With four polar capsules.--
_Chloromyxidæ._

(2) Amœboid germ with a vacuole stainable with iodine. Spores with
two polar capsules.--_Myxobolidæ._

For further subdivisions the differences in the spores are
principally utilized.

Order. *Microsporidia*, Balbiani.

These are the organisms discovered in the stickleback by Gluge in
1834, and in _Coccus hesperidum_ by Leydig in 1853. They have since
been found in numerous other arthropods, especially insects. They
acquired particular importance when it was discovered that they
were the cause of the “pébrine” disease (“gattina” of the Italians)
which caused so much destruction amongst silkworms (_Bombyx mori_).
Pasteur (1867–70) and especially Balbiani (1866) participated in the
researches on _Nosema bombycis_, and it was the latter who classed
the “pébrine bodies” or “psorospermia of the arthropoda” amongst the
Sporozoa as Microsporidia (1882).[223] The complete life cycle of
_N. bombycis_ was described in 1909 by Stempell. The Microsporidia
are not confined to insects and arachnoids, they are now known to
occur also in crustacea, worms, bryozoa, fishes, amphibians and
reptiles. Certain tumours in fishes, similar to those formed by many
Myxosporidia, are produced by Microsporidia. Fantham and Porter found
that _Nosema apis_ was pathogenic to bees and other insects, and
was the causal agent of the so-called “Isle of Wight” disease in
bees[224] in Great Britain.

[223] _C. R. Acad. Sci._, Paris, xcv, p. 1168.

[224] _Annals Trop. Med. and Parasitol._, vi, pp. 145–214, 3 pls.

The Microsporidia, as their name implies, form minute spores which
usually are oval or pear-shaped. Each spore contains a single polar
capsule which is not easily visible in the fresh state (fig. 98, _f_)
and a single amœboid germ issues from the spore (fig. 99, _b_).

The life cycle of _Nosema apis_, parasitic in bees, may be taken
as an example of that of a microsporidian. The infection of the
host is initiated by the ingestion of spores of _N. apis_ in food
or drink contaminated with the excrement of other infected bees.
Under the influence of the digestive juice of the bee the spore-coat
(sporocyst) softens, the polar filament is ejected and anchors the
spore to the gut epithelium, and the minute amœbula contained in the
spore emerges. The amœbula is capable of active amœboid movements
(fig. 98, _b_) and so is termed the planont or wandering form
(fig. 98, _a_). After a short time each planont penetrates between
or into the cells of the epithelium of the gut, a few only passing
through into the body cavity. Within the cells the amœbulæ become
more or less rounded, lose their power of movement, and after a
period of growth of the trophozoite (fig. 98, _c_) commence to divide
actively, these dividing forms being known as meronts (fig. 98,
_d_). Various forms of fission occur, and during this phase, termed
merogony, the numbers of the parasite within the host are greatly
increased, with concomitant destruction of the epithelium (fig. 98,
_e_). After a time sporogony commences. The full-grown meront becomes
successively the pansporoblast and sporoblast. Nuclear multiplication
and differentiation ensue and five nuclei are ultimately produced. At
the same time a sporocyst is secreted, and two vacuoles are produced
within. One is the polar capsule, and within it the polar filament
is differentiated; the other forms the posterior vacuole (fig. 98,
_g_). Between the two vacuoles the body cytoplasm or sporoplasm forms
a girdle-like mass. Of the nuclei, one regulates the polar capsule,
two control the secretion of the sporocyst, and two remain in the
sporoplasm. The polar capsule and polar filament are not usually
visible in the fresh condition, but can be demonstrated by the use
of various chemical reagents (fig. 100). The sporoplasm ultimately
becomes the amœbula (fig. 98, _g_) which issues from the spore after
the ejection of the polar filament.

A trophozoite (meront) of _N. apis_ becomes a single pansporoblast
which gives rise to one sporoblast producing one spore, and this
procedure is characteristic of the genus _Nosema_. In other genera
the trophozoite may form more than one pansporoblast and each
pansporoblast may form a variable number of spores in different
cases. Various attempts at classification have been based on these
characteristics. It must suffice here to note that in the cases where
the trophozoite becomes one pansporoblast, the latter can produce
four spores in the genus _Gurleya_, eight spores in _Thélohania_ and
many spores in _Pleistophora_. In other cases, where the trophozoites
give rise to many pansporoblasts, each of the latter may form many
spores, as in the genus _Glugea_.

A few pathogenic microsporidian parasites other than _N. apis_ may
be mentioned. _N. bombycis_, causing pébrine in silkworms, may
infect any or all the tissues of the host (fig. 99). The larvæ of
the host, _i.e._, the “silkworms,” may become infected by eating
food contaminated with spore-containing excrement of already
infected silkworms. In cases of heavy infection the silkworm dies,
but should the infection be less intense the larva becomes a pupa
in which the parasite persists, so that the moth emerges from the
cocoon already infected. Not only is the moth parasitized itself,
but the Nosema reaches the generative organs of both sexes and
penetrates the ovaries of the female, with the result that the ova
are deposited infected. Such infected eggs are capable of developing,
so that infection may be transmitted hereditarily as well as by the
contaminative method. Infected eggs can be recognized by microscopic
examination, as Pasteur showed, and thus preventive measures may be
adopted.

A microsporidian parasite is known to occur on the roots of the
spinal and cranial nerves of _Lophius piscatorius_, the angler fish.
This parasite is variously referred to the genera _Nosema_ and
_Glugea_.

_Thélohania contejeani_, parasitic in the muscles of crayfish, is
believed by some to be the causal agent of recent epizoötics among
them, though others believe the disease to be really due to a
bacillus. It may be that the one organism aids in the entry of the
other into the host.

Order. *Actinomyxidia*, Stolč.

A brief mention may be made of the Actinomyxidia (fig. 101), which
were first described by Stolč in 1899 as parasites of Oligochætes.
They have also been investigated by Mrazek, and a detailed study
of certain species was made by Caullery and Mesnil (1905). The
trophozoite is small and amœboid. The spores are large, and exhibit
tri-radiate symmetry. Spore formation is complicated and sexual
processes occur therein. Many amœbulæ are set free from each spore.

Order. *Sarcosporidia*, Balbiani.

The first member of this group was discovered by Miescher in 1843.
This author found white filaments running parallel with the direction
of the fibres in the voluntary muscles of mice. They were visible
to the naked eye, and proved to be cylindrical tubes tapering at
each end. They were as long as the muscular fibres, were enveloped
in a membrane, and contained innumerable elongate or kidney-shaped
bodies and a smaller number of little spherical forms. Th. v.
Hessling confirmed (1853) the occurrence of these “Miescher’s tubes”
within the muscular fibres, this author having discovered the same
structures in the heart muscles of deer, cattle, and sheep. Both
investigators considered them to be pathological transformations of
the muscles. v. Siebold, from his own experiences, regarded them as
fungus-like entophytes.

Rainey (1858) discovered similar structures in the muscular system
of pigs, and considered them to be early stages of _Cysticercus
cellulosæ_, which error Leuckart rectified, simultaneously
emphasizing their relationship with Myxosporidia. Both these authors
found them in the muscular fibres, and both observed that they
possessed a thick striated membrane. Manz (1867) published the
results of more minute investigations on the structure and contents
of the cylinders. This observer also recognized the disease in
rabbits and attempted to cultivate the parasites. He also tried to
induce experimental infection in guinea-pigs, rats, and mice, but the
result was negative.

However, domestic and wild mammals are not the only hosts of
Sarcosporidia; these parasites are also harboured by birds. Thus,
according to Kühn, they are found in the domestic fowl; according
to Rivolta in _Turdus_, _Corvus_, and other birds; according to
Stiles in North American birds; while Fantham found Sarcosporidia
in the African mouse-bird, _Colius_. Reptiles also are parasitized
occasionally. Bertram found them in the gecko, Lühe in the
wall-lizard. It was found also that the Sarcosporidia could develop
not only in the muscles but also in the connective tissue. This
led to the foundation of a new, but provisional, classification by
Blanchard, using the generic name _Miescheria_ for the parasites
in the muscles and _Balbiania_ for those in the connective tissue.
Finally, Sarcosporidia have also been observed in man.

The relation of these parasites to certain diseases of domestic
animals has been studied by veterinary surgeons. Sarcosporidia may
cause fatal epizoötics among sheep.

There is still a wide field open for research in regard to the
structure and development of these parasites, and the manner in which
the hosts become infected.

The Sarcosporidia usually appear as elongate, cylindrical, or fusiform bodies, rounded at both extremities and of various lengths and breadths (fig. 102). In some species they may be from 16 mm. to 50 mm. long, as in the sheep and roebuck. These bodies are the so-called sarcocysts or Miescher’s tubes. They lie in transversely striated muscular fibres which they distend more or less. The forms found in the connective tissue are apparently parasites which originally inhabited the muscular fibres, and only on disintegration of the fibres reached the connective tissue, where they grow to large oval or globular bodies (fig. 105). The mammalian muscles usually infected are those of the œsophagus, larynx, diaphragm, body-wall, and the psoas muscles. The skeletal muscles may be affected in acute cases, as well as those of the tongue and eye. The heart muscles are sometimes parasitized.

In fresh material cut into thin slices the parasites are
frequently recognizable, even with the naked eye, because of their
yellowish-white colour. Under the microscope they appear to be
coarsely granular (fig. 103). Beginners may find some difficulty
in distinguishing them from other foreign bodies, such as dead and
calcified encapsuled Trichinæ, or from Cysticerci that have died
and become calcified in the early stages, more particularly as the
Sarcosporidia also occasionally may become calcified.

The Sarcosporidia are always enveloped in a membrane, which is probably formed at an early stage. In a few cases it remains thin and simple, in other cases a radially striated ectoplasmic layer is present (figs. 104, 108), which has been variously described. From the inner integument, which may be homogeneous or fibrous, thick or thin, membranes or trabeculæ pass into the interior of the body, forming anastomosing partitions, and so producing a system of chambers of various sizes that do not communicate with one another (figs. 104, 108). These chambers are occupied by sickle- or bean-shaped bodies (spores or sporozoites), or various developmental stages of them. The oldest spores are found in the centre of the Miescher’s tubes or trophozoites. If they are not liberated they die there, so that the central chambers of the tube are empty and hollow.

In the youngest Sarcosporidia (40 µ in length) from the muscles of the sheep there occur, according to Bertram, small roundish or oval cells (4 µ to 5 µ), the nuclei of which are half their size, and are embedded in a granular protoplasmic mass. In somewhat larger, and therefore older, cylinders, the investing membrane of which already shows both layers, the cells have become larger (to 7 µ) and are more sharply outlined from each other (fig. 106). These uninucleate cells may be considered as pansporoblasts. In each pansporoblast division of the nucleus occurs (fig. 107), and meanwhile the pansporoblasts become isolated within the chambers, the dividing partitions of which originate from the granular protoplasm which is present between the pansporoblasts. The numerous uninucleate daughter forms produced within the chambers become spores direct (fig. 108).

The process commences in the centre of the cylinders or sarcocysts, and then progresses towards the extremities, the parasites meanwhile increasing in size, and new pansporoblasts being continually formed at the extremities (fig. 107).

The spores (sometimes called Rainey’s corpuscles), vary in shape according to the species, but are also of different form individually. They are mostly kidney-, bean- or sickle-shaped (fig. 109), and of small size, sometimes reaching 14 µ by 3 µ to 5 µ. They are apparently surrounded by a thin membrane, and at one extremity (according to the discovery of L. Pfeiffer, confirmed by van Eecke, Laveran and Mesnil) contain an obliquely striated body (fig. 109) often homologized with the polar capsule, while the greater part of the spore is taken up by the nucleate sporozoite. Several authors state that they have also observed filamentous appendages (polar filaments) at one end of the spores, and have seen two kinds of spores in the same Sarcosporidium. Spores of various species of Sarcosporidia may contain metachromatic granules, often centrally placed (fig. 109). These granules may be metabolic or possibly may contain toxin (see below).

The gymnospores of _Sarcocystis muris_, from the mouse, show active boring movements when kept in saline solution warmed to 35° or 37° C. _S. muris_ is very deadly to its host. From their structure the spores do not appear to have great powers of resistance to external conditions. They measure 12 µ by 3 µ to 4 µ or less.

Laveran and Mesnil (1899) isolated a toxin from _S. tenella_ of the sheep and called it sarcocystin. This substance is especially pathogenic to experimental rabbits.

The duration of life of the Sarcosporidia is a comparatively long one. The affected muscular fibres may remain intact and capable of performing their functions for a long time, but at last they perish, if the host lives long enough. Thus the Sarcosporidia of the muscles are then enveloped only by sarcolemma, and finally, when this likewise disappears, they fall into the intra-muscular connective tissue. In many cases the Sarcosporidia die off within their hosts, this, according to Bertram, being brought about by a disintegration of the spores in the central chambers. In other cases the leucocytes play a part in the destruction of the Sarcosporidia, and sometimes it happens that lime salts are deposited in and around the vacant cylinders.

In some places pigs, sheep, mice and rats are infected with sarcosporidiosis to a remarkable extent, in certain cases almost reaching 100 per cent. Young animals also are infected, and perhaps infection only takes place during youth.

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The Animal Parasites of ManChapter XII: Appendix: “Rhizopods in Poliomyelitis acuta.” (6)

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