116
I.—Inoculation of Animals with the soiled blood of the Rat.
The first experiments were made with equines, but subsequently many investigations with other
species of animals were taken in hand. Between December 1890 and February 1892, twelve horses
were subcutaneously inoculated with a small quantity of blood (1 to 2 c.c.) containing the hæmatozoon
in varying numbers. Of these, four animals or 33.3 per cent. contracted Surra :—
No.
„
„
„
IX.—
XXVIII.—
XLII—
LXII—
Period of incubation lasted
„
„
„
„
„
„
18
29
13
63
days, animal lived 19 days.
„
„
„
2
2
5
„
„
„
Of the remaining eight animals, four (Nos. LII, XIII, XII, XLVIII) were re-inoculated with soiled
rat's blood, but with negative results a second time. It was later determined to test certain of these
horses with Horse Surra blood, in order to determine whether any protection had been conferred from
the previous inoculations with the rat hæmatozoon, and find whether .the course of the subsequent
disease would be modified in any way. For this purpose five animals were selected, three (Nos. XIII,
XII, XLVIII) submitted on two, and two (Nos. XLVI, LVIII) on one occasion only to subcutaneous
injections of rat's blood.
TABLE XXXV.
Horse
Number.
XIII
XII
XLVIII
XLVI
LVIII
Fluid used.
Blood ...
„
„ ..
„
„
...
Quantity
used.
c.c.
1.0
m. j
0.5
1.0
3.0
How administered.
Directly into jugular
vein,
Subcutaneously
Do.
Do.
Do.
A.M. or
P.M.
A.M.
A.M.
A.M.
P.M.
P.M.
From what Animal.
Horse XIX
Do
Horse L
Do. XLVIII
...
Do. XLVII
Date of
Inoculation.
29
5
12
23
29
4
4
21
11
3
91
91
91
91
92
Date of first
appeance
hæmatozoon
7
11
22
1
7
5
4
11
12
4
91
91
91
91
91
Latest
period,
length in
days.
8
6
10
8
9
Death
12
26
23
7
3
6
4
11
12
5
91
91
91
91
91
Days
between
the first
appearance
of hæma-
tozoa and
death.
36
16
1
6
27
It will be observed that far from the previous inoculation of rat's blood in any way producing
immunity or modifying the disease in the horses, it (certainly) accelerated the course of the malady in
several of the animals, and produced more virulent symptoms and pathological changes. So that we
may assert that horses unsuccessfully inoculated and re-inoculated with the rat hæmatozoon, when
subsequently inoculated with Horse Surra blood, show no protection from the former, but acquire the
disease after an incubation period of six to ten days.
Although the latent period of Rat Surra was so prolonged in the first instance when inoculated
from rat to horse—average 31 days,—it immediately returned to the normal period—average 7 to 8
days,—when a second horse was inoculated with the blood of the first affected. The latent period, how-
ever, becomes still more reduced, 5 days, when a third animal is inoculated with the blood of the second.
II.— The Gastric ingestion of rat's excrement.
The question as to how rats could cause Surra in horses was raised; for the food would rarely, if
ever, be soiled with the blood of these animals.
The following experiments were, therefore, undertaken with a view to ascertain whether the excreta
of rats—in whose blood the infusorian was present at the time of its collection—could produce the
disease when mixed with the grain of the horses under experiment. For this purpose, numerous rats
were obtained, the blood of each being submitted to careful microscopical examination, and those
animals in which the hæmatozoon was found to be present were placed in an iron wire-cage by them-
selves. When a sufficient number of these latter were obtained, the cage was placed over a metal plate,
and the excrement which fell through was collected in the morning and evening, and mixed with the
corn, and was given to the animals under experiment at 8 A.M. and 6 P.M. Every week the blood of the
caged rats was again submitted to microscopical examination, and those in which the hæmatozoon
was found to be absent, were discarded, and their places filled by fresh ones in which the organisms
were found to be numerous.
It was recognised before commencing the. experiment in Poona that the result might probably
prove negative, on account of the dryness of the situation, but it was nevertheless considered worthy of
a trial.
The first experiment, (Horse No. LXXV) was commenced on the morning of the 26th November
1892, and was continued until the evening of the 7th February 1893, a period of seventy-four days.
Small doses (grammes iii) were given at first, but these were varied later according to the amount of
excrement obtainable. During the whole course of the case, the temperature never exceeded 38.1 °C.
except on two occasions. One might have been inclined to consider the negative result in this case as
clear evidence of the innocuous properties of rat-dung, and its inability to produce Surra, but before
doing so several points must be taken into consideration.