Chapter III: Its Control and Suppression (3)

1. The bubo was aspirated by means of a sterile hypodermic
syringe. The material thus obtained was placed in the water
of condensation of an agar-slant culture tube.

2. At least 7 centimetres of blood were withdrawn from the
_cubital_ vein by means of another sterile syringe, and 5
centimetres of it were placed in an Erlenmeyer's flask,
containing 200 centimetres of neutral meat broth. The rest of
the blood was emptied into a sterile tube, and used for
agglutination tests.

Cultures obtained by this method were examined
microscopically, and the growths on various culture media
were studied. Gram stain, Löffler's methylene blue, and
hanging-drop method were used. Polar-staining and chain
formation in liquid media and the characteristic type of
colony on the surface of agar were looked for. Animal
inoculation was performed in every case, and the culture
isolated from each case was identified by agglutination test,
rabbit's immune serum being used.

The results of the bacteriological examination of a series of
24 patients are tabulated in the two following tables. Table
I includes the fatal cases and Table II those cases which
recovered.

The diagnosis of plague could be safely made from the
microscopical examination of the liquid aspirated from the
bubo in the majority of the cases. However, in certain
instances the amount of the aspirated fluid being small and
the bacilli very few, it was impossible to diagnose the case,
especially when the cultures from the bubo were negative.
Repeated examination of the patient was necessary under those
conditions, but it happened in cases 22 and 23 that the
patients died of plague before a second examination could be
made. The smears and cultures from case 22 remained sterile,
while the smears and cultures made from the swelling on the
neck of patient 23 revealed the presence of pneumococci. Both
patients died of plague, as was ascertained by examination of
the organs after death.

TABLE I.--EXAMINATION OF FATAL CASES OF PLAGUE

========================================================================
|Date of Examination 1912
| +--------------------------
| |Duration of illness _Days_
| | +----------------------
| | |Hours before death
| | | +----------------
| | | | Bubo
| | | |Smear
| | | | Culture
| | | | Animal
| | | | inoculation
| | | | +----------
| | | | | Blood
| | | | |Culture
| | | Age | | | | | Aggluti-
Patient | Race |Sex |_Years_| | | | | nation
--------------+--------+----+-------+--------+---+-----+-----+----------
1. Sing Nu |Chinese |Male| (?) |July 11| 5 | 48 |+ + +|0 0
| | | | | | | |
3. Aluncion | | | | | | | |
Raymundo |Filipino|Male| 15 |Sept. 29| 3 | ... |+ + +|0 0
| | | | | | | |
4. Filo | | | | | | | |
Almalas |Filipino|Male| 39 |Oct. 10| 4 | 22 |+ + +|+ -
| | | | | | | |
6. Polycarpio| | | | | | | |
Guzman |Filipino|Male| 34 |Oct. 22| 2 | ... |+ + +|0 0
| | | | | | | |
7. José | | | | | | | |
Sarmiento |Filipino|Male| 37 |Oct. 22| 3 | ... |+ + +|0 0
| | | | | | | |
8. Julian | | | | | | | |
Gonzales |Filipino|Male| 41 |Oct. 22| 3 | 23½ |0 0 0|+ -
| | | | | | | |
9. Valeriano | | | | | | | |
Buencamino|Filipino|Male| 31 |Oct. 22| 3 | 10 |+ + +|+ -
| | | | | | | |
10. Pedro | | | | | | | |
Nicomedes |Filipino|Male| 30 |Oct. 22| 2 | 5¾ |+ + +|+ -
| | | | | | | |
12. Regino | | | | | | | |
Gulano |Filipino|Male| 34 |{Oct. 22| 2 |106 |0 0 0|+ -
| | | |{Oct. 24| 4 | 82 |0 0 0|0 0
| | | | | | | |
13. Martin | | | | | | | |
Dimalanta |Filipino|Male| 35 |Oct. 23| 3 | 25½ |+ + +|+ -
| | | | | | | |
14. Roberto | | | | | | | |
Obiso |Filipino|Male| 5 |Oct. 23| 1 | 53 |+ + +|+ -
| | | | | | | |
15. Juan | | | | | | | |
Barceta |Filipino|Male| 23 |Oct. 24| 3 | 37 |+ + +|+ -
| | | | | | | |
16. Yu Tum |Chinese |Male| 14 |Oct. 24| 2 | ... |+ + +|0 0
| | | | | | | |
17. Augustin | | | | | | | |
Monterey |Filipino|Male| 29 |Nov. 1| 1 | 27 |+ + +|+ -
| | | | | | | |
18. Demetrio | | | | | | | |
Pabraw |Filipino|Male| 27 |Nov. 23| 4 | 15 |0 0 0|+ -
| | | | | | | |
21. Ambrosio | | | | | | | |
Sobremonte|Filipino|Male| 20 |Dec. 7| 6 | 1 |+ + +|+ -
| | | | | | | |
22. Mateo | | | | | | | |
Marcelo |Filipino|Male| 8 |Aug. 20 |(?)| ... |- - -|0 0
| | | | | | | |
23. Alejandro | | | | | | | |
Gita |Filipino|Male| [A]17 |Nov. 24 | 3 | ... |- - -|0 0
--------------+--------+----+-------+--------+---+-----+-----+----------

========================================================================
|Date of Examination 1912
| +--------------------------
| |Duration of illness _Days_
| | +----------------------
| | |Hours before death
| | | +----------------
| | | | Skin
| | | |Smear
| | | | Culture
| | | | Animal
| | | | inoculation
| | | | +----------
| | | | | Sputum
| | | | |Smear
| | | | | Culture
| | | | | Animal
| | | Age | | | | | inocu-
Patient | Race |Sex |_Years_| | | | | lation
--------------+--------+----+-------+--------+---+-----+-----+----------
1. Sing Nu |Chinese |Male| (?) |July 11| 5 | 48 |+ + +|- - -
| | | | | | | |
3. Aluncion | | | | | | | |
Raymundo |Filipino|Male| 15 |Sept. 29| 3 | ... |0 0 0|0 0 0
| | | | | | | |
4. Filo | | | | | | | |
Almalas |Filipino|Male| 39 |Oct. 10| 4 | 22 |+ + +|0 0 0
| | | | | | | |
6. Polycarpio| | | | | | | |
Guzman |Filipino|Male| 34 |Oct. 22| 2 | ... |0 0 0|0 0 0
| | | | | | | |
7. José | | | | | | | |
Sarmiento |Filipino|Male| 37 |Oct. 22| 3 | ... |0 0 0|0 0 0
| | | | | | | |
8. Julian | | | | | | | |
Gonzales |Filipino|Male| 41 |Oct. 22| 3 | 23½ |0 0 0|+ + +
| | | | | | | |
9. Valeriano | | | | | | | |
Buencamino|Filipino|Male| 31 |Oct. 22| 3 | 10 |0 0 0|0 0 0
| | | | | | | |
10. Pedro | | | | | | | |
Nicomedes |Filipino|Male| 30 |Oct. 22| 2 | 5¾ |0 0 0|0 0 0
| | | | | | | |
12. Regino | | | | | | | |
Gulano |Filipino|Male| 34 |{Oct. 22| 2 |106 |0 0 0|0 0 0
| | | |{Oct. 24| 4 | 82 |0 0 0|+ + +
| | | | | | | |
13. Martin | | | | | | | |
Dimalanta |Filipino|Male| 35 |Oct. 23| 3 | 25½ |0 0 0|0 0 0
| | | | | | | |
14. Roberto | | | | | | | |
Obiso |Filipino|Male| 25 |Oct. 23| 1 | 53 |0 0 0|0 0 0
| | | | | | | |
15. Juan | | | | | | | |
Barceta |Filipino|Male| 23 |Oct. 24| 3 | 37 |0 0 0|0 0 0
| | | | | | | |
16. Yu Tum |Chinese |Male| 14 |Oct. 24| 2 | ... |0 0 0|0 0 0
| | | | | | | |
17. Augustin | | | | | | | |
Monterey |Filipino|Male| 29 |Nov. 1| 1 | 27 |0 0 0|0 0 0
| | | | | | | |
18. Demetrio | | | | | | | |
Pabraw |Filipino|Male| 27 |Nov. 23| 4 | 15 |+ + +|0 0 0
| | | | | | | |
21. Ambrosio | | | | | | | |
Sobremonte|Filipino|Male| 20 |Dec. 7| 6 | 1 |0 0 0|0 0 0
| | | | | | | |
22. Mateo | | | | | | | |
Marcelo |Filipino|Male| 8 |Aug. 20 |(?)| ... |0 0 0|0 0 0
| | | | | | | |
23. Alejandro | | | | | | | |
Gita |Filipino|Male| [A]17 |Nov. 24 | 3 | ... |0 0 0|0 0 0
--------------+--------+----+-------+--------+---+-----+-----+----------

[A] Months.

TABLE II.--EXAMINATION OF PLAGUE PATIENTS WHO RECOVERED

=========================================================================
|Date of examination 1912
| +-----------------------
| |Duration of disease
| | +----------------
| | | Bubo
| | |Smear
| | | Culture
| | | Animal
| | | inoculation
| | | +----------
| | | | Blood
| | | |Culture
| | | Age | | | | Aggluti-
Patient | Race | Sex |_Years_| | | | nation
----------------+--------+------+-------+--------+------+-----+----------
| | | | 1912 |_Days_| |
| | | |{Sept.29| 2 |- - -|0 0
| | | |{Oct. 2| 5 |+ + +|0 0
2. Dionisio |Filipino|Male | 18 |{Oct. 3| 6 |0 0 0|- +1:16
Capate | | | |{Oct. 7| 10 |- - -|0 0
| | | |{Oct. 15| 18 |- - -|- +1:64
| | | | | | |
5. Alejandra |European|Female| 6 |Oct. 20| 7 |+ + +|0 0
Fisher | | | | | | |
| | | |{Oct. 22| 2 |+ + +|+ -
| | | |{Oct. 24| 4 |+ + +|0 0
11. Gabriel |Filipino|Male | 21 |{Oct. 26| 6 |0 0 0|- +1:16
Sevilla | | | |{Nov. 8| 18 |- - -|0 0
| | | |{Nov. 15| 25 |- - -|- +1:64
| | | | | | |
| | | |{Nov. 26| 3 |+ + +|+ -
| | | |{Dec. 6| 13 |0 0 0|- +1:32
19. Esteban |Filipino|Male | 15 |{Dec. 16| 23 |- - -|- +1:60
Roa | | | |{ 1913 | | |
| | | |{Jan. 11| 48 |- - -|- +1:120
| | | | | | |
| | | |{Dec. 2| (?) |+ + +|0 0
20. Sia Su |Chinese |Male | 35 |{Dec. 5| -- |0 0 0|+ -
| | | |{Dec. 16| -- |- - -|- +1:80
| | | | | | |
24. Purificacion|Filipino|Female| 19 |{Dec. 11| 3 |+ + +|0 0
del Val | | | |{Feb. 11| 33 |- - -|0 0
----------------+--------+------+-------+--------------------------------
NOTE.--The bubo in Nos. 2, 5, and 24 never opened
spontaneously. The pus was aspirated at the time of the
second, eventually third, examination. Nos. 11 and 19 opened
spontaneously. A fistula formed along the canal which was
caused by the puncture, and healed up in several weeks. Hard
inguinal buboes of secondary order persisted in patient 19 at
the time of second examination. No plague bacilli were found
either in the bubo of the first or second order. Patient 20
had a considerable amount of pus in the inguinal primary bubo,
but it was not opened until after the last examination.

Two of the patients, cases 8 and 12, had numerous plague
bacilli in the sputum at the time when the expectoration
showed the presence of blood (twenty-three and one-half and
eighty-two hours, respectively, before death). In 3 cases I
was able to prove the presence of _Bacillus pestis_ in the
skin lesions, _intra vitam_, fifteen, twenty-two, and
forty-eight hours, respectively, before death. In case 18
there was no doubt that the skin lesions, which covered the
whole body and the face, were of secondary nature, as the
patient died shortly afterward. It was undoubtedly a case
similar to those reported by Gotschlich and Zabolotny.[5] In
the other two patients there was only 1 maculopapulous
efflorescence on the foot in case 1 (with a corresponding
femoral bubo) and 2 lesions of the same type on the arm and
forearm in case 4 (with a corresponding axillary bubo). It is
possible that these lesions were the original port of entry of
infection. Numerous plague bacilli were found in the skin
lesions of these cases, both microscopically and in culture.

[5] Kolle und Wassermann: Handbuch der pathogenen
Mikroorganismen. Gustav Fischer, Jena (1903), =2=, 521.

The plague patients tabulated in Table II recovered. They
were all treated with antiplague serum. While cases 5, 11, 19,
and 24 appeared clinically to be rather severe, cases 2 and
20 were mild.

It can be seen from the table that the plague bacilli may not
be detected in the enlarged gland at first (case 2) and that
their presence may be revealed only after repeated
examination of the bubo. It is also evident from the results
of repeated examinations that the plague bacilli disappear
from the infected gland in a comparatively short time, as a
rule at the time when pus starts to form. Contrary to the
findings in patients who died, distinct phagocytosis was
noticed in the smears made from the aspirated liquid in those
patients who recovered and who had been treated with serum
soon after the onset of the disease. It is undoubtedly this
process that clears the gland of the infectious agents.

The general opinion in regard to the presence of _Bacillus
pestis_ in the circulating blood seems to have been, as
Thompson remarks, that "the bacillus is rarely to be found in
the peripheral blood stream before the agonal stage."[6]

[6] Journ. Hyg., Cambridge (1906), =6=, 558.

The Austrian Commission, using few drops of blood, found
positive blood culture in 40 per cent; Calvert in Manila in
100 per cent when examined twenty-four hours before death;
Choksy, Berestneff, and Mayr in 45 per cent; and Greig in 60
per cent. The Indian Commission examined 28 patients, and
obtained positive blood cultures in 16 out of 23 fatal cases.
Not a single positive blood culture was obtained from the
patients who survived. The time of blood examination in
positive cases was three and one-half to seventy-five and
one-half hours before death. The amount of blood used was 1
cubic centimetre. Only 6 out of the 30 samples, which gave
positive blood culture, were found positive by microscopical
examination of blood smears. The following conclusions are
based on these observations in regard to the septicæmic stage
of bubonic plague: (1) "A severe septicæmia may be present
at a comparatively early stage of the disease and for a
considerable number of hours before death, and (2) the
septicæmia may be of an irregular and fluctuating type."[7]

[7] _Ibid._ (1907), =7=, 395.

From the tables it will be seen that out of 15 patients
examined by me, 14 gave positive blood culture; and of these
3 recovered. One blood culture revealed the presence of
streptococcus in addition to _Bacillus pestis_. The results
of the examinations tabulated in Tables I and II show, in
agreement with the findings of the Indian Commission, the
occasional early occurrence of plague bacilli in the blood
stream, as the time of examination in the positive cases
varied from one hour to one hundred six hours before death.
In consideration of the ephemeral character of the septicæmic
stage of plague, as evidenced by repeated blood cultures in
the three patients who recovered, one can hardly avoid the
impression that there is a certain degree of septicæmia in
every case of plague. The possibility of detecting the
bacillus in the circulating blood increases in proportion
with the quantity of blood used for culture. The best chance
to recover plague bacilli from the circulating blood seems to
be in the stage of high fever and general prostration.

The phenomenon of agglutination of plague bacilli by the
serum of patients was first observed by Wissokowitsch and
Zabolotny in 1897[8] and later confirmed by the German Plague
Commission. Vagedes, Klein, and others[8] pointed out the
defects of the reaction as a diagnostic means. Aside from
the technical difficulties, the reaction was found
inconstant, and its occurrence was not noticed until the
second week of the disease and even then only in low
dilutions of the serum.

[8] Referred to in Kolle und Wassermann: Handbuch der
pathogenen Mikroorganismen (1903), =2=, 524.

Although the recent work of Strong[9] and of Strong and
Teague[10] has reduced the technical difficulties, the fact
remains that positive agglutination of plague bacilli by the
patient's serum cannot be obtained in the first week of the
disease, and, therefore, the isolation of plague bacilli from
the body of the patient is still the only quick and safe
method of plague diagnosis.

[9] The Philippine Journal of Science, Sec. B. (1907), =2=,
155.

[10] _Ibid._ (1912), =7=, 194-201.

Having utilized the technic devised by Teague, I have had no
difficulty in performing the agglutination test in plague.
The emulsion of plague bacilli, to be used for the test, was
prepared by suspending young cultures of virulent plague
bacilli, grown at 30° C., in salt solution and filtering the
suspension through filter paper. No antiseptic was added nor
heat applied. Serial dilutions of unheated patient's serum
were mixed with equal amounts of bacterial suspension in
small test tubes. Incubation at 35° C. followed. Controls,
consisting of serial dilutions of normal human serum as well
as bacterial suspensions without serum, excluded any possible
error which might have been caused by spontaneous
sedimentation of the bacterial suspension; while a parallel
test with highly agglutinant serum facilitated the reading of
positive results.

Altogether, 22 tests were performed on 15 patients, 11 of
whom were fatal cases and 4 of whom recovered. In the
negative reactions, the duration of the disease at the time
of examination ranges from two to six days. The non-fatal
cases showed slight agglutination from the sixth day on. From
that day, the agglutination titer of the serum was found to
rise, and the agglutinins persisted in the blood of
convalescents up to the seventh week of the disease.[11]

[11] It is hoped that it will be possible to examine some of
the survivors for agglutination from time to time.

It must be borne in mind that the patients, who showed
positive agglutination, had been vigorously treated with
antiplague serum. Nevertheless, in consideration of the low
titer of the curative serum (dilution 1:32, agglutination
positive; dilution 1:64, agglutination negative), the rise of
the agglutinant power of the patient's serum in dilutions
higher than 1:16 cannot be explained as wholly due to passive
immunity, but rather to active immunity arrived at on the
principle of simultaneous immunization.

From the preceding observations the following conclusions are
drawn:

1. The importance of blood cultures as a diagnostic means is
evident from the fact that positive blood culture was
obtained in practically every case that was examined in the
febrile stage of the disease, even when buboes or signs of
pulmonary involvement had not been detected clinically.

2. It is also evident that _Bacillus pestis_ may be found in
the circulating blood of the patients even in cases which
subsequently recover.

3. The period of time during which _Bacillus pestis_
circulates in the blood is evidently short and irregular.

4. Mixed infection may be encountered in plague septicæmia
(_Streptococcus_, _Pneumococcus_).

5. The agglutination test is of no value for the diagnosis of
plague, as it was found positive only in convalescents.

6. Phagocytosis of plague bacilli in the bubo was noticed
only in patients who recovered after being vigorously treated
with curative serum.

7. The presence of numerous plague bacilli in comparatively
insignificant skin lesions during the life of the patient
points to the possibility of direct transmission, while the
fact that a patient without any apparent bubo, who is not so
sick as to be detained from his daily occupation, may
expectorate large numbers of plague bacilli, are facts of
great importance with regard to the communication of the
disease. It is obvious that the last-mentioned condition
might, and very likely does, give rise to an epidemic of
pneumonic plague if the atmospheric and sanitary conditions
are favorable.

TABLE III.--INSECTS FOUND TO CONTAIN BACILLUS PESTIS

====================================================================== | | |Experi- | | |mental Author | Insect | Source of infection |trans- | | |mission ---------------+---------------+---------------------------+---------- Yersin |Flies |Laboratory infection | Nuttal |Flies |Experimental infection | Nuttal |Bedbugs |Experimental infection |Negative | | | by bite. Nuttal |Flea |Experimental infection |Negative. Hankin |Ant's fæces |Fed on plague material | Hankin |Bedbugs |Plague hospital | Ogata |Flea |Plague rats | Simond |Flea |Plague rats, experimental |Positive. Tindswell, 1900|Flea |Plague rats |Negative. Tindswell, 1903|Flea |Plague rats |Negative. Kolle |Flea |Experimental infection |Negative. Gauthier and |Flea |Experimental infection |Positive. Raybaud | | | Liston |Flea |Epidemic among pigs; | | | harbored fleas; | | | dead rats found |Positive. Zirolia |Flea |Retained _Bacillus pestis_,| | | 7-8 days | British |Flea |Repeated experiments |Positive. Commission | | | Verbijtski |Flea and bedbug|Experimental infection |Positive. La Bonadière |Fly | | and | | | Xanthopulides| | | Herzog |_Pediculus |Dead body of plague case | | capitis_ | | ---------------+---------------+---------------------------+----------

II. OBSERVATIONS ON THE TRANSMISSION OF PLAGUE BY
BLOOD-SUCKING INSECTS

Judging from the data which have been collected from the
literature[12] on the transmission of plague (Table III),
Simond seems to have been the first to call attention to
the important part which blood-sucking insects, particularly
fleas, play in the transmission of plague. Although many
investigators have been successful in demonstrating the
presence of _Bacillus pestis_ in the digestive system of
blood-sucking insects, it was not until the experiments of
Gauthier and Raybaud that the actual transmission of plague
infection by fleas was convincingly proved. Ever since the
exhaustive and conclusive experiments, which were carried out
both under natural and artificial conditions by the British
Plague Commission, and the work of Verbijtski, which antedates
the British Commission, were presented, there has been no
doubt that the transmission of plague by blood-sucking
insects, particularly by the fleas, is one, although not the
only, mode of spreading this disease. It is obvious, as Herzog
correctly remarks, that the factors which are responsible for
the spreading of plague must be considered individually in
each epidemic and in various parts of the world as well. There
is no doubt that the importance of any insect in the
transmission of plague depends on its habits as well as on
those of the host, be it either animal or man.

[12] Centralbl. f. Backt., 1 Abt. (1897), =22=, 87, 437.
Report of Indian Plague Commission (1898-99). Zeitschr. f.
Hyg. u. Infectionskrankh. (1901), =36=, 89. Kolle und
Wassermann: Handbuch der pathogenen Mikroorganismen (1903),
=2=, 538. Zeitschr. f. Hyg. u. Infectionskrankh. (1905), =51=,
268. Journ. Hyg., Cambridge (1907-10), plague numbers. _Ibid._
(1908), =8=, 162, 260.

During the recent outbreak of plague in Manila, several
samples of bed-bugs from the beds of the plague patients and
dog fleas from a plague-infected house were collected and
examined, but with negative result.

In spite of the fact that it adds nothing new to the question
of whether or not plague can be transmitted by fleas, since
the question has been conclusively answered by the work of
the Indian Commission, nevertheless the following
observations of a small outbreak of plague among animals, the
spreading of which was due solely to fleas, are of interest.

One wild rat was inoculated with strain Iloilo 3 of
_Bacillus pestis_. The skin adjoining the root of the right
ear was scarified, and a loopful of the culture was smeared
on the scarified skin. The rat was found dead three days
after the inoculation.

The cage containing the dead rat was immersed in kreolin
solution. At autopsy the cervical glands were found slightly
swollen, somewhat reddened, but no hæmorrhagic œdema of the
surrounding tissue was noticeable. There was slight necrosis
at the place of inoculation, showing superficial, purulent
discharge. Clear effusion in both pleural cavities and one
hemorrhage in the pleura were found. The lungs were
hyperæmic, but otherwise normal. The spleen was of somewhat
darker color, but otherwise normal in size and appearance.
The liver showed a slight degree of parenchymatous
degeneration, the congestion making prominent the structure
of the organ. The typical, although not constant, changes of
the organ, which are characteristic of natural plague
infection in rats, were absent. The kidneys were without
macroscopic change. The lymph glands, with exception of the
cervical nodes, were normal.

Examination of the rat's fur revealed ectoparasites on the
neck, under the chin, and back of the ears; these at the time
of the examination apparently were dead. About 6 common rat
fleas were found and identified as _Lœmopsylla cheopis_
Rothsch. The parasites were immersed in sterile salt solution
for three hours. When removed in a dry test tube, they began
to move about sluggishly. The intestinal tract of these fleas
contained blood.

Five of the fleas were crushed by means of sterile forceps,
and inserted in a pocket under the shaved skin of a
guinea-pig. The animal died of plague within three days,
showing considerable hemorrhagic œdema around the place of
inoculation, typical bilateral inguinal buboes, and
characteristic changes in the spleen. Smears and cultures
made from the bubo and spleen were positive for _Bacillus
pestis_.

Another wild rat, which was in a separate cage in the same
room where rat 1 had been kept, died twenty-four hours after
rat 1. The two cages were at least 10 centimetres apart. Rat
2 harbored fleas of the same species as were found on rat 1.

Numerous severe bites were detected back of the ears and on
the neck of the dead animal. The post-mortem findings were
identical with those described in rat 1; that is, cervical
buboes, pleural effusion, and slightly enlarged spleen.

It is well to remark that both rats had been kept in the same
room for about six months. Fleas had never been noticed on
our guinea-pigs. During the time the rats had been kept in
the plague house no irregular results were noticed in
plague-inoculated animals. At the time the first rat was
inoculated no other plague-infected animals were in the
plague house, and since that time another building has been
used for plague-infected animals.

Two days after the death of rat 2 three guinea-pigs, which
were kept in separate cages in the same room, were found dead
of plague (smears and cultures were both positive). Several
fleas (_Lœmopsylla cheopis_) were found on the necks of these
animals. They were collected and inoculated in the same way
as the fleas from the first rat. The experimental animal,
which was inoculated with the fleas, was killed and found to
be infected with plague. The findings were local reaction,
inguinal buboes, and typical spleen. Smears and cultures were
positive for _Bacillus pestis_.

Although numerous healthy guinea-pigs were examined in the
same plague house, no fleas could be found at that time, only
the 2 rats and the first 3 guinea-pigs are positively known
to have harbored fleas, the latter after the death of the
rats and not before.

The gross lesions in these naturally infected guinea-pigs
were somewhat unlike those found in guinea-pigs infected
either by vaccination or by intraperitoneal or subcutaneous
inoculation. All except one showed primary buboes on the neck
with more or less extensive hemorrhagic œdema extending in
some cases over the thorax. There was little pleural effusion
present; the spleen always showed typical changes of necrotic
foci varying in size and number. In one instance similar foci
were found also in the liver, large enough to be visible
macroscopically. This was in a case where like changes were
found in the lungs.

Only one of the guinea-pigs showed an exception, in that the
primary buboes were located in the inguinal region, with
pelvic and axillary glands secondarily involved. These are
the findings usually met within guinea-pigs artificially
infected with plague by the vaccination method, if the lower
part of the abdomen be chosen for inoculation. The reason for
such a deviation from the findings in the rest of the
guinea-pigs may lie in the fact that this animal was almost
completely deprived of hair by a skin disease.

It is of importance to mention the skin lesions which were
found on the necks of the guinea-pigs, particularly under the
chin. Besides small red spots which appeared to be fresh flea
bites, small, elevated, and fairly deep infiltrations partly
covered with moist scab were found in the skin under the
chin. Other animals showed changes usually found in the
scarified skin of guinea-pigs after artificial inoculation
with plague material. The base of each cutaneous
efflorescence was hemorrhagic and œdematous.

A histological study of the tissues of these guinea-pigs
known to be naturally infected by plague fleas showed the
following changes:

THE CERVICAL BUBO.--The enlarged lymphatic gland was
surrounded with a thickened capsule. Necrosis existed in the
subcapsular part of the gland, where it formed an almost
continuous circular zone, leaving the central part less
changed. Smaller irregular necrotic foci were scattered
throughout the section. Polymorphonuclears in various stages
of disintegration were found throughout the section.

_The Lungs._--Very few blood extravasations were present in
the alveoli; otherwise normal.

_The Spleen._--The capsule was thin. There were subcapsular
hemorrhages. The Malpighian bodies were somewhat enlarged,
but of normal structure. Throughout the parenchyma irregular
multiple necrotic foci were found, leaving but little of
spleen tissue intact. Numerous polymorphonuclears which were
present showed varying degrees of karyorrhexis.

_The Kidneys._--The outline of the cells was indefinite; a
few miliary hemorrhages existed in the cortical part of the
organ.

_The Liver._--There was excessive congestion, fatty
degeneration, and pigmentation of the cells. The capsule was
slightly thickened.

_The Skin._--The epithelium was missing in one place in the
section, and cellular infiltration extended from that place
into the subepithelial layer of the surrounding skin. The
same kind of infiltration reached deep into the skin, stripes
of cellular infiltration penetrating into the tissue along
the muscle fibres. There was no direct connection between the
cellular infiltration and the follicles of the hair.

It may be well to describe in detail the time of death from
plague among these and the other animals in this outbreak, as
well as the time when the plague house was disinfected.

The first animal (rat 1) having been inoculated on August 27,
in the afternoon, died of plague within three days (August
30). The second animal (rat 2) died twenty-four hours later.
Guinea-pigs 3, 4, and 5 (see plan) were found dead on the
morning of September 2; that is, two days after the death of
rat 2 and three days after the death of rat 1.

The same day that the three guinea-pigs were found dead of
plague, rooms I, III, IV, and VI were thoroughly disinfected.
The floor, the ceiling, and the walls were sprayed with
kerosene and lysol solution. The remaining animals in room VI
were destroyed, and the cages disinfected. No animals were
kept in rooms I, III, and IV at that time.

Three days after the death of animal 5, guinea-pigs 6 and 7
were found dead of plague, while the next day guinea-pigs 8
and 9 died. No death occurred on September 7, but the next
two days each recorded two plague guinea-pigs (10, 11, 12,
and 13). On September 11, the last guinea-pig died of plague
in this outbreak. The whole building was then thoroughly
disinfected. No plague-inoculated animals were kept in the
rooms after the first sign of the epidemic. After September
11, no more cases of spontaneous plague infection were
observed.

It will be noticed that the epidemic lasted eleven days
after the first animal died and fourteen days after animal 1
was inoculated. Altogether, 14 animals out of at least 200
animals exposed died of plague.

No death occurred among rabbits, although these animals were
distributed among the guinea-pigs. In fact, 2 rabbits were
surrounded by plague guinea-pigs 8, 9, and 10, but did not
contract plague.

From the epidemiological standpoint it is interesting to know
the dimensions and location of the cages in which the animals
were kept.

Aside from the 2 rats which were confined in ordinary traps
that stood on a table 80 centimetres high, the rest of the
animals were kept in regular metal animal cages. The
dimensions of the cages are: Fifty centimetres long, 36
centimetres broad, and 30 centimetres high. The cage stands
on four legs each 10 centimetres long; the centre of the
bottom of the cage holds a drain opening 8 centimetres above
the floor.

The majority of the cages in room II were located on the
floor; some on the second shelf of a wooden rack. This
last-mentioned arrangement, judging from the construction of
the wooden frame, allowed a continuous passageway for the
fleas to the second shelf of the racks. On the other hand,
the deaths among the guinea-pigs in room V were restricted to
the cages standing on the floor, the majority of cages in
that room being placed on tables 80 centimetres high.

Only a theoretical explanation can be given of the short
duration and sudden cessation of the outbreak. One can assume
with great probability that the first partial disinfection
drove the fleas away from the primary source of infection,
and that they traveled as far as possible. They finally
settled in those guinea-pig cages which had not been molested
by the first disinfection. Having no new supply of plague
blood (all of the plague-infected guinea-pigs having been
removed, most of them before death), the fleas soon cleared
themselves of plague bacilli. The peculiar feature of the
outbreak, namely, the failure to find fleas on the animals in
rooms II and V, finds its explanation in the observation of
the Indian Commission who found that the fleas "died or
disappeared very rapidly."

The following conclusions can be drawn from these
observations:

1. The common rat flea (_Lœmopsylla cheopis_) prefers the rat
to the guinea-pig.

2. In the absence of rats it will attack guinea-pigs rather
than rabbits.

3. The fleas which have sucked blood from rats or guinea-pigs
afflicted with plague septicæmia were found to harbor
virulent plague bacilli inside of their bodies.

4. The transmission of plague infection by direct or indirect
contact being excluded in our case, the fact that fleas of
the same species and harboring plague bacilli were found on
the rat and on the guinea-pigs, the presence of flea bites on
the rats and on the guinea-pigs with positive findings of
skin lesions on that part of the body where the fleas and
flea bites were located, together with the anatomical picture
of the findings in the guinea-pigs, lead to but one
explanation; namely, that the plague infection was
transmitted by fleas.

III. OBSERVATIONS ON ANIMALS SUSPECTED OF PLAGUE

Out of the several tens of thousands of rodents examined
during the antirat campaign, we have found only two plague
rats which showed the typical picture of natural plague
infection in rat; that is, cervical buboes with surrounding
œdema, subcutaneous injection, pleural effusion, enlarged
spleen, and such changes of the liver as are characteristic
of natural plague infection in rats. Microscopically, large
numbers of plague bacilli were found in these cases, and pure
cultures of _Bacillus pestis_ were recovered from the spleen.
Histological examination of internal organs, particularly
that of the liver, confirmed the bacteriological findings.
The remainder of the plague rats exhibited only two of the
signs of plague infection, namely, bubo and œdema of the
surrounding tissue, and eventually hemorrhages.

Besides plague infection, a great number of rats showed
purulent conditions from causes other than plague. Abscesses
of the lungs were frequently met with, and cervical or
axillary buboes are not uncommon in Manila rats. Various
pyogenic bacteria were found in the pus of such abscesses. Of
the less common was _Bacillus pyocyaneus_ and the
pneumobacillus of Friedländer. Chronic plague was excluded in
these cases since the animal inoculation failed to produce
plague infection.

More than half of the rats examined harbored parasites in
their organs. _Echinococcus taeniæformis_ was found in the
liver of practically every gray rat, while a small _Ascaris_
and _Tænia diminuta_ were not uncommon in the intestines. Two
rats were found to have sarcosporidiosis, 2.6 per cent.
showed rat leprosy, and 7.4 per cent. trypanosomiasis. One
tumor of the mammary gland and one tumor in the axillary
region were encountered, while one tumor of the large
curvature of the stomach proved to be a chronic inflammatory
tumor due to parasites. One peritoneal tumor in a rat (_Mus
decumanus_) gave the impression of a malignant tumor on
account of the miliary dissemination of the peritoneum. It
was found to consist of muscle and spindle-cell sarcomatous
tissue. Ectoparasites were very seldom noticed, on account of
the method of collecting the rats. When present, they were
mites and fleas.

In the naturally infected plague rats the rigidity of the
fresh cadaver was pronounced. The primary bubo was in every
case cervical. Cervical glands were enlarged and hemorrhagic
with slight œdema of the surrounding tissue. The subcutaneous
injection extended over the neck and chest. The inguinal
glands were small and pigmented. The lungs were collapsed,
and showed hemorrhagic foci. The spleen was slightly
enlarged, firm, and dark red. The liver was rather large,
firm, pale red, with shade of yellow, which was caused by
minute yellowish foci thickly scattered throughout the tissue
and visible through the capsule. The kidneys were hyperæmic.
The intestines were without change. The serous membranes were
pale with no hemorrhages.

Histological examination of the tissue of naturally infected
plague rats showed the following changes:

_Liver._--The structure of the organ was well marked; the
veins dilated, trabeculæ slightly compressed, nuclei well
stained, and few of the liver cells showed vacuoles. Small
foci, most numerous under Glisson's capsule, were scattered
throughout the organ; they varied in size, but were not
larger than a miliary tubercle. The small necrotic foci were
found to consist of few necrotic liver cells. The centre of
the larger foci was formed by degenerated and necrotic liver
tissue, surrounded by round-cell infiltration.
Polymorphonuclears were also found in the zone of cellular
infiltration. There was a slight degree of hemorrhage in
each focus. Epithelioid cells and large vesicular cells with
several nuclei were to be found. The foci, mentioned above,
were sharply demarcated from the surrounding liver tissue,
which appeared to be intact.

_Spleen._--The structure was well preserved, the capsule
thin. The Malpighian bodies were normal as to the elements of
which they consist. Cells with pycnotic nuclei were scattered
throughout the organ, and vesicular cells with small, deeply
stained, excentrically located nuclei were present.
Polymorphonuclears were found in the tissue in considerable
numbers. No localized necrotic foci could be found in
sections through the spleen.

_Cervical Glands._--The blood-vessels were considerably
distended. A few hemorrhages and polymorphonuclears were
present. Œdema of the capsules and surrounding tissue
existed. Part of the gland was necrotic.

_Lungs._--The blood-vessels were distended. The alveoli
contained homogeneous masses and blood. There were numerous
subpleural hemorrhages. The bronchi were collapsed, and
contained mucus.

_Kidneys._--The cortical part showed subdued structure; the
epithelial cells had an indefinite outline and occasionally
showed vacuolization. The medullar part was better preserved.
There were miliary subcapsular hemorrhages. A few small foci
were scattered throughout both medullar and cortical parts.
They consisted of round-cell infiltration.

NATURAL PLAGUE INFECTION IN A CAT

The experiments of the German Plague Commission proved that
cats showed considerable resistance to plague infection as
cutaneous and subcutaneous inoculations failed to infect
them. According to the Austrian Commission, cats develop
submaxillary buboes if fed on plague material. They are said
by Albrecht and Gohn[13] sometimes to recover. Out of four
cats fed on plague material two died of plague, one showing
submaxillary, the other mesenterial buboes. Virulent plague
bacilli were found in the discharge from the nose and also in
the fæces of cats which apparently did not become infected
after having been fed on plague material.

[13] Über die Beulenpest in Bombay im Jahre 1897 (1897), II
B, II C.

One case of spontaneous plague infection of a cat was
recorded by Thompson[14] in Sydney.

[14] Report of an outbreak in Sydney, 1900. Referred to in
Kolle and Wassermann (1903), =2=, 510.

W. Hunter,[15] in Hongkong made observations on cats
suffering from plague infection. The author also undertook a
few experiments, and arrived at the following conclusions:

1. Cats suffer from plague.

2. The disease may be acute or chronic.

3. The type of the disease is septicæmic.

4. The animals may occasionally play a part in the
dissemination of plague.

5. In plague-infected areas cats probably become infected
through rats, which they devour as food.

6. In plague-infected districts possible plague infection in
cats is of great importance from a domestic point of view.

[15] Lancet (1905), =I=, 1064.

On November 27, 1912, a sick cat was brought to the
laboratory for examination. It was reported that the animal
was found in a warehouse in which dead rats had been found
some time previously. The rats were not examined. In the
morning of the 30th, the cat was found dead in the cage where
it had been kept under observation. The following are the
post-mortem findings:

The animal was a fairly well-nourished female.[16] The
subcutaneous tissue, pericardium, mediastinum, and
mesenterium contained considerable amounts of fat.

[16] The cat was the mother of 4 kittens which were about 3
weeks old at the time the cat was delivered for examination.
They were kept under observation for several weeks, but
showed no signs of plague infection.

The subcutaneous tissue of the neck showed œdema and small
hemorrhages. The submaxillary tissues were swollen on both
sides. When the fasciæ and superficial muscles of the neck
were removed, enlarged glands were found on both sides. These
were closely attached to the submaxillary salivary glands.
The surrounding tissue was œdematous, but no hemorrhages were
noticed in the vicinity of the enlarged glands. Upon section
the glands were found to be necrotic, and upon pressure a
thin purulent liquid escaped. There were no hemorrhages
within the glands. Several enlarged lymph-nodes, smaller in
size, could be followed down the neck on the left side. The
lymph-nodes in the axillæ as well as in the groins and
peribronchial nodes were normal. The mesenteric glands were
slightly enlarged and reddened.

The lungs were slightly collapsed. A clear, sanguineous,
slightly coagulated effusion was observed in both pleural
cavities. The tissue of the lungs showed considerable œdema
and hypostasis. The bronchi and pharynx showed no changes,
the mucous membrane being pale and thin.

The heart was normal.

The spleen was enlarged, of light red color, with follicles
slightly prominent.

The stomach contents was blackish in color; there were no
hemorrhages or ulcers in the mucosa.

The liver was somewhat enlarged. The organ showed prominent
structure, the centres of the acini being red, the periphery
lighter in color.

The kidneys were slightly enlarged and pale. The capsule
peeled off easily, the venæ stellatæ were prominent, the
surface smooth; there were no hemorrhages. The cortex was
increased in breadth and was of the same color as the
surface; the pyramids were darker in color. The organ was of
fragile consistence.

Suprarenals were normal, as were also intestine and bladder.

The histological findings were as follows:

_Bubo._--The capsule of the gland was œdematous. The whole
gland as seen in cross section had undergone necrosis, except
a few foci which still showed cellular structure.

_Lungs._--The alveoli were filled with homogeneous masses,
containing but few degenerated epithelial cells and
leucocytes. The blood-vessels were dilated, particularly in
the subpleural part of the organ. In some places capillary
mycotic emboli with subsequent hemorrhage were encountered.
The large blood-vessels and bronchi were normal.

_Salivary Glands._--Those glands attached to the primary bubo
showed the normal structure of a combined mucous and serous
gland.

_Liver._--There was considerable congestion. The centres of
the acini showed parenchymatous and fatty degeneration. The
cells on the periphery of the acini exhibited typical fatty
infiltration. The large blood-vessels and small ducts were
without change.

_Kidney._--The cells of the kidney showed various degrees of
degeneration, ranging from parenchymatous to fatty
infiltration. There were a few capillary hemorrhages and
hyaline casts present.

_Suprarenals._--These showed slight degeneration.

_Spleen._--This organ showed congestion, a few hemorrhages,
and bacterial emboli; otherwise normal.

The bacteriological examination of the material from this cat
gave the following results:

1. _Smears:_

_a._ From the buboes showed degenerated leucocytes, many
lymphocytes, and numerous bacteria, some of which resembled
_Bacillus pestis_ in their polar staining.

_b._ From the spleen showed numerous plague-like,
polar-stained bacilli. Round involution forms were present.

2. _Cultures:_

_a._ From the buboes were badly contaminated with _Bacillus
coli_ and _Bacillus pyocyaneus_ colonies.

_b._ From the spleen: A few scattered colonies of _Bacillus
pyocyaneus_ developed on the surface of the agar. Between the
large colonies a scanty growth of dewy appearance was
noticed. Smears made from this growth revealed plague-like
bacilli of the cultural type, showing a few club-shaped
involution forms. Subcultures were made in order to secure
pure culture. They showed a pure growth of _Bacillus pestis_
as indicated by the morphology of bacilli and shape of the
colonies. Agglutination with plague-immune serum was
positive.

3. _Inoculation experiments (vaccination method):_

_a._ One guinea-pig was inoculated with the material from the
left bubo, another one with material from the right bubo.
They died of plague on the third and fifth days,
respectively.

_b._ One guinea-pig was inoculated with the material from the
spleen. It died of plague on the third day.

_c._ One guinea-pig was inoculated with material from the
nostrils obtained by swab. The animal survived, showing no
indication of plague.

_d._ One guinea-pig was inoculated with material from the
rectum obtained by swab. It died of plague on the fifth day.

Although plague infection among cats is apparently a rare
occurrence, the fact that cats may contract the disease in
spite of the high degree of resistance to plague infection
has to be considered from the hygienic standpoint.

To appreciate the important rôle which cats may play in the
spreading of the disease one need only consider the close
contact of these animals with rats on one side and human
beings on the other. It is also a well-established fact that
not only plague-infected cats, but also those which have
devoured plague-infected material and remained apparently
normal, may excrete plague bacilli which have retained their
full virulence.

NOTES ON PLAGUE IN HONG KONG BY DR. ROBERG.--During the Hong Kong epidemic of plague which preceded and was coincident with that of Manila, I visited that city twice (December, 1913, and July, 1914), but I did not closely investigate the methods adopted and carried out by the authorities there, for the reason that the Manila plan was so much more productive of results, as shown by the apparent inability of the Hong Kong officials to gain control of the disease. However, I received from Dr. David Roberg, of the Oregon State Board of Health, a copy of a report made by him to the Secretary of his State Board of Health, following an investigation of the Hong Kong epidemic and the methods there followed. I have Dr. Roberg's permission to use his report and it is herewith presented. It is dated Manila, April 16, 1914, and is as follows:

I have the following notes to present on the epidemic of
bubonic plague in Hongkong.

On April 5th when I arrived in Hongkong the epidemic was
rapidly approaching its height. With its onset in January
there were 47 cases, in February 42, and in March 223. During
the week previous to April 5th, there were 91 cases; during
the six days I was in Hongkong they averaged 15 a day.

Judging from previous epidemics the present one will be
exceptionally severe. The season for the occurrence of human
plague is from the months of February to July. The onset is
gradual; in May it reaches its maximum and then declines. In
the epidemic of 1912, for the city of Victoria the monthly
rate showed the following, January 9, February 22, March 61,
April 265, May 513, June 346, July 105, August 11, and
September 1. Comparing these rates with those of the present
year it will be seen that the number for March far exceeds
that of two years previous.

Illustrating the season for human plague, with its onset,
maximum and decline, are the monthly rates for the city of
Kowloon during 1912, when the following cases occurred:
February 2, March 12, April 52, May 246, June 152, July 39,
August 8, and September 3.

The season for human cases is determined by the condition of
the rats. At the close of the season in July the rats die off
from plague in great numbers as it is then the hottest time
of the year. During the months from September to February the
rats increase in number and in susceptibility to the extent
of being sufficient to again infect human beings. Moreover
every other year shows a marked severity in the epidemics of
human bubonic plague. This is explained by the fact that it
requires two years' time for the rat population to become of
sufficient greatness and susceptibility to cause a severe
human outbreak. This is shown by the yearly number of cases
since the year 1911. During the years 1911, 1912 and 1913
respectively, there were 253, 1847, and 408 cases. During the
present year the monthly rate is exceeding that of the heavy
year of 1912.

The severe epidemic in 1912 was a result of the influx of
50,000 Chinese refugees into Hongkong during the revolution
in 1911. The number of rats in the native district depends
upon the available food supply, and as a result of this human
overcrowding the amount of waste food so increased in the
houses, yards and streets, that the over accumulation of
garbage could not be kept pace with. This influx also brought
in great numbers of susceptible rats.

The number of rats killed off during the epidemic in 1912
were so great that in 1913 they had not recovered
sufficiently to cause a severe outbreak during that year, and
as a result of the lightness of epidemic in 1913, they are so
increased in number and susceptibility now that they are
causing a very severe epidemic in human beings.

Of rats in Hongkong they have the _Mus decumanus_ or drain
rat and the _Mus rattus_ or house rat. It is noteworthy that
the drain rat is found plague-infected throughout the year,
while the house rat is found infected only during the period
in which the human epidemics occur, namely from February to
July. The number of infected rats a year run parallel to the
number of monthly cases.

The bulk of human infection is due to the spread of house
rats. Man also becomes infected by the drain rat when the
drains are flooded by rain storms and the rats are driven
into the houses.

What has made plague permanent in Hongkong is the
overcrowding of the native districts. Besides there is a
floating population entering and leaving the native quarters,
numbering about 4000 a day. The native houses have been built
with double floors and walls which harbor the rats. Where the
construction is of wood it is possible to remove the rat
spaces. It has been found since the introduction of plague
into Hongkong in 1894, that those districts containing the
greatest number of soft brick houses with hollow walls, have
shown the greatest incidence of plague. This can not be
remedied as it would involve the destruction of buildings on
too large a scale.

THE WORK OF THE SANITARY BOARD

The area under the control of the Board comprises the Island
of Hongkong containing 32 square miles, with a sea frontage
of 13 miles in length. Included also is the old city of
Kowloon which is situated one mile and a third across the
harbor and contains two and three-fourths square miles. The
city of Victoria on the northern shore of the Island of
Hongkong has a sea frontage of 5 miles, contains about ten
thousand domestic buildings, of which about one thousand are
non-Chinese.

The population of Hongkong is difficult to estimate, as the
floating population is so great. In the 1912 census there
were 446,614 Chinese and 21,163 non-Chinese.

The city of Victoria is divided into 10 Urban Health
Districts and old Kowloon into 2. There is an inspector in
charge of each. These districts are built over an area
averaging from 31 to 140 acres. The houses in these districts
average one thousand and the population from 8000 to 33,000.
There are four inspectors in charge of the scavenging work,
one for the disinfection stations in Victoria and old
Kowloon, one for the cemeteries and two for general duty.

The measures employed by the Sanitary Board are summarized as
follows: