2 5 6 
Rabbits do not show any symptoms, ’but remain quite healthy and well- 
nourished. The trypanosomes are never very plentiful, and usually show 
periodicity. Two rabbits which died had extensive coccidiosis, and their death in 
less than four months after inoculation was probably due to this secondary 
infection. 
Post-mortem .—The spleen is slightly enlarged and rather congested. The 
lymphatic glands are usually quite pale, firm, and only very slightly enlarged 
Guinea-pigs (3). 
The incubation period is prolonged and the disease is also of long duration- 
up to 139 days. The animals remain quite healthy and the temperature does not 
rise during the disease. The trypanosomes are rather scanty at first, but before 
death occurs they increase in number and may finally be fairly plentiful. At the 
autopsy of those dead of the disease the spleen is found to be enlarged and rather 
soft. The lymphatic glands are increased in sixe to a slight extent and are quite 
pale in colour. 
Rats (14). 
Rats are rather susceptible to the disease. The incubation period is short, 
from five to fourteen days. It is interesting to note that in the rat sub-inoculated 
directly from the steer (Yolo No. 9) trypanosomes were not seen until the lapse of 
2 49 days. When once established, the disease runs a chronic course as a rule, 
lasting for from 40 to 254 days. The usual length is about 80 days. The parasites 
are scanty, but usually increase in numbers before the animal's death. Periodicity 
is marked ; the parasites may be absent from the blood for two or three weeks 
Ihe mode of inoculation has no influence on the incubation period. Large doses 
may cause the parasites to appear a little sooner than they otherwise would, but 
rats inoculated with such doses do not die any more quickly than those inoculated 
with small doses of infected blood. The quick passage of the trypanosome through 
a succession of rats (six) did not increase the virulence in any way. 
Post-mortem .— The spleen is enlarged, congested and rather firm. The 
lymphatic glands are slightly larger than normal, and are quite pale and firm- 
The other organs show no changes. 
Mice (2). 
As in rats, the incubation period is short, about four days, and the disease is 
chronic. One mouse is alive 219 days after inoculation and still infected. The 
trypanosomes are ahvay r s scanty, and may be absent from the peripheral blood 
stream for many days— 78 on one occasion. The post-mortem changes are similar 
to those found in rats. 
It will thus be evident that most of the common laboratory animals 
are susceptible to the infection. Mice and rats are most easily infected, 
guinea-pigs least. 1 he disease is chronic and lasts for a comparativel) 
long time. It produces few or no symptoms and the trypanosomes 
are usually present in but small numbers. The strain is not very 
virulent, and resembles in this the strain derived from the horse. 
(<£) Horse trypa nosomes 
The animal reactions of the strain derived from the second horse, 
Toul, are epitomised briefly below. 
