258 
No symptoms of any sort are noticeable in guinea-pigs. The virulence ol the 
strain was not increased by successive passages through three guinea-pigs; the 
incubation period and the duration of the disease were not affected. The tempera¬ 
ture chart does not reveal any rise during the course of the affection. The 
trypanosomes are usually rather scanty, but before the death of the animal they 
may increase in numbers until they are fairly plentiful. 
At the autopsy a more or less marked enlargement of the spleen was seer: 
The organ was congested and rather soft. The lymphatic glands, as a rule, were 
unchanged, though in a few instances they were slightly enlarged and in one case 
haemorrhagic. The other organs appeared normal. 
Rats (io). 
Rats are rather susceptible to the disease. The incubation period varies 
between one and forty-one days ; as a general rule it is about four to six days. The 
duration of the disease varied from nine to 253 days, usually about 70. In the 
acute cases the parasites are present continuously until death, and are usually 
fairly numerous. In the chronic cases periodicity is observed and the trypano¬ 
somes, when present in the peripheral circulation, are usually in small numbers. 
Increase in the virulence of the strain was not obtained by passage through a 
succession of four rats. Sub-inoculations made from other experimental animals 
became infected in approximately the same time. 
Post-mortem .— The spleen is enlarged and is congested and soft in consistence. 
Haemorrhagic infarcts were seen in one case. The lymphatic glands may or may 
not be enlarged. The enlargement is usually slight when it is present. The 
glands are pale and rather firm. The other organs normal. In one case subpleural 
petechiae were observed. 
Mice (2). 
As in rats, the incubation period is short, in our experiments about two days. 
I he disease is chronic and lasts for months—as long as five. When first present 
the trypanosomes are very scanty. They disappear in a few days and may not be 
seen again in the peripheral blood for weeks. In one case they were absent for 
fourteen. They reappear before death and increase in number until the animal 
succumbs. 
Post-mortem. The spleen is very much enlarged, congested, dark purple in 
colour, and rather soft in consistence. The lymphatic glands are not enlarged. 
The other organs appear normal. 
In general, the trypanosome is not very virulent. The incubation 
period is prolonged and, while the disease has always terminated 
fatally, death only ensues after the lapse of a comparatively long 
interval. The low degree of virulence is also manifested by the lack 
of symptoms and the absence of heightened temperature in the 
experimental animals. Efforts to increase the virulence by successive 
passages through any one species of animal (four passages) or through 
an alternation of animals, e.g., guinea-pigs, and rats (three of each; 
were without result. The parasites are scanty, as a rule, and in the 
more chronic cases exhibit periodicity in a very marked degree. 
In the following sections the cattle trypanosomes in the Congo 
Free State are treated as a whole. 
