112
SECTION III.
Description of Experimental Researches, and Results of the same obtained at Poona.
In 1890, as no statistics were forthcoming with regard to the percentage of rats which contained
the 'Trypanosoma' in their blood, it was determined to make a careful microscopical examination of
the blood of as many of these animals as possible. The results arrived at were as follows.
From November 1890 to May 1892, the blood of 349 rats was examined microscopically, hæmato-
zoa were found present in 106, and absent in 234, giving a percentage of 30.37 present, 69.63 absent.
At a later date the elucidation of further details was required, especially with regard to the num-
ber of organisms present in the circulation of each individual animal.
Naturally, when the number of organisms had to be determined, the easiest way would have been
to use one of the Hæmocytometers for that purpose, but in practice it was found to be useless, for when
very few parasites were present in the circulation of an animal, it frequently happened that although
several could be observed in cover-glass preparations of blood, none could be found in the small quan-
tity used for examination with the Hæmocytometer. Consequently, the number of parasites present in
the samples of blood examined were expressed in terms of few (1 in a specimen to 5 in each field of
the microscope with Zeiss Ocular IV, and Objective D), numerous (5 to 20), very numerous (20 to
50) and swarming over 50 in each field. The Trypanosoma in several fields of the microscope were
counted and the mean taken.
In this way from June 1892 to July 1894, the blood of 758 rats was
submitted to examination with the following results:—
TABLE No. XXIX.
Showing the Rats (Mus decumanus) examined from June 1892 to July 1894, and the relative
number of organisms in their circulation.
In field of microscope .
Number of rats
Percentage
...
...
Absent.
...
443
58.44
Few.
1—5
107
14.12
Numerous.
5—20
66
8.71
Very
numerous.
20—50
66
8.71
Swarming.
Over 50
76
10.02
Total rats
examined.
...
758
100.00
Present.
...
315
41.56
Absent.
...
443
5844
If we divide the Bombay year into two periods, (i) dry and hot (January to May inclusive), (ii)
rainy and humid (June to December inclusive) we find that during the period November 1890 to
July 1894, 421 out of a total of 1,107 rats examined contained the hæmatozoon in their circulation.
It was present in 31.53 per cent. of the rats caught from January to May, and 40.31 per cent. of those
obtained from June to December, or during the rainy season. Although in the hot season the hæma-
tozoon is present in the circulation of these animals, the organisms are very few in number, while
during the latter period of the year they are far more numerous, the percentage of cases in which the
hæmatozoa were very numerous or swarming being 24.00 in the dry season and 52.61 in the rainy
season, or a ratio of 1: 2.19.
From the above facts it became evident that the ' Surra' months, or those during which the disease
appeared in equines, and those in which the blood of rats presented the maximum number of hæma-
tozoa, were identical, viz. the monsoon or rainy season, which varies according to the year, commenc-
ing in June or July and terminating in September or October. Consequently, during the following
year we collected as many rats as possible during each month, with a view to determine the percentage
of animals in which the parasite was present. At first there was some difficulty in obtaining so great
a number of rodents, but at last we enlisted quite an army of helpers and at the end of the following
April found our total 2,102.
The following table explains itself :—
TABLE No.
XXX.
Showing the total number of Rats (Mus decumanus) examined in each month from May 1894 to the
end of April 1895, with the relative number of hæmatozoa in their circulation.
Month.
May...
June
...
...
July...
August
September ...
October
November ....
December ...
Absent.
33
42
66
107
96
156
88
166
Few.
9
6
21
31
24
44
26
37
Nume¬
rous.
4
1
15
7
20
22
6
15
Very
nume-
rous.
1
4
10
21
15
15
7
12
Swarm-
ing.
1
5
12
22
24
25
14
22
Absent.
33
42
66
107
96
156
88
166
Present.
15
16
58
81
83
106
53
86
Total.
48
58
124
188
179
262
141
252