26 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
agglutination. If these animals were bled very freely, a new inoculation of virulent 
blood would cause them to become infected, and after that the disease pursued the 
normal course. The spleens of rat 285 and some of the five others not showing the 
infection were small and normal looking, the glands were not enlarged. The spleens 
ot rats dying after a duration of more than two weeks are very markedly enlarged, as 
pointed out by Laveran and Mesnil. The glands are also enlarged and many, 
especially the retroperitoneal group, are haemorrhagic. The pleural surface of the 
lungs is very often spotted with small petechial haemorrhages. Oedema has only been 
noticed on two occasions. Paralysis has never been noted in rats dying from the 
acute form. Two rats suffering from the chronic form developed a partial paresis of 
the left-hind leg. Haemorrhagic nephritis has been noted in two large rats suffering 
from the chronic type, the urine contained a tew trypanosomes, the kidneys showing 
numerous small haemorrhages on their surface and in their substance. 
Mice — White, Black, and Grey 
The incubation varies from two to five days. Death may occur in the acute 
cases within sixteen to twenty-three days. In the more chronic cases the duration may 
be from thirty-seven to one hundred and thirty days. In the acute cases the parasites 
appear and continue to augment almost up to death. In the chronic phase of the 
disease there is very often a marked periodicity, the parasites being absent from the 
blood for intervals of eight to fourteen days. Subinoculations at such a time into 
young rats or mice are negative if small amounts of blood are used. 
Two mice inoculated intraperitoneally with blood from Horse VI (p. 30) in 
amounts of 1*5 to 2'0 c.c, the blood being negative to microscopic examination, never 
showed parasites until the fourteenth and fifteenth days, the parasites then began to 
increase and the disease terminated eight days after the appearance of trypanosomes. 
Two mice were inoculated from the horse at the same time and never became infected, 
but were later on shown to be immune. 
As Laveran and Mesnil note, the spleens of mice infected may become 
enormously enlarged. The organ often being six times as large as normal, causes a most 
noticeable tumour and almost completely filling the abdominal cavity compresses the 
other organs. In mice treated with arsenic the splenic tumour has lessened at the 
same time as the parasites have temporarily disappeared from the blood. 
Guinea-Pigs 
Over twenty-five have been used. The incubation has varied between four to 
fifteen days, the average being four to six days. The duration of the disease is from 
nine to sixty days. The acute cases showing parasites in large numbers in the blood 
very often die in thirteen to twenty days. Young guinea-pigs succumb sooner than 
do adults. There is usually a slight rise of temperature on the appearance of 
