#910. | T. gambiense and T. rhodesiense in Lats, ete. 209 
number of parasites inoculated in the case of each strain was approximately 
the same. 
The average life of rats inoculated with 7. rhodesiense was 11°3 days, 
whereas the life of rats infected with 7. gambiense was 13°8 days. (The 
average weight of the rats inoculated with 7. rhodesiense was 138°8 grammes, 
of those infected with 7. gambiense, 137 grammes.) 
The number of divisions of parasites occurring in the first 24 hours in both 
strains averaged 6, and varied in each case from 2 to 10 divisions, being most 
frequently about 8. 
There is a shorter period between the crests of the waves in the graphs 
denoting the number of trypanosomes in the Rhodesian strain (about 
three to four days) than in the laboratory strain of 7. gambiense (namely, 
four to six days). The Rhodesian strain, then, was the more virulent. 
Guinea-pigs.—Daily counts were made of five guinea-pigs inoculated with 
T. rhodesiense (see Chart 4), and of five guinea-pigs inoculated with 
T. gambiense (see Chart 5). The duration of life (averaging 59 days) of 
those inoculated with the Rhodesian strain was shorter than in those 
inoculated with 7’. gambiense (averaging 111 days). In guinea-pigs the 
disease tended to run a chronic course. The periods between the crests 
of the waves in both strains in guinea-pigs were longer than in rats, namely, 
five to eight days, and the initial rise was slower. 
Rabbits—Two rabbits were inoculated with 7. rhodesiense. They lived 
29 and 24 days respectively. Periodic variation occurred in the numbers 
of the parasites, especially in one case. These animals exhibited an affection 
of the eyes and skin, there being a white purulent discharge from the eyes, 
and the skin at the roots of the ears became encrusted with scabs. 
The periodicity in the numbers of the parasites in the peripheral circulation 
of infected animals is to be explained by (@) variations in resistance on the 
part of the host, probably due to the formation of anti-bodies; accompanied 
by (0) the formation on the part of the trypanosomes of rounded, latent, 
non-flagellate (relatively resistant) forms in the internal organs of the host 
during the fall in numbers of the parasites in the peripheral blood. 
There is, therefore, a life-cycle of trypanosomes in the vertebrate host, in 
addition to stages of the parasite in the invertebrate carrier (e.g. Glossina). 
