1910.| Sickness studied by Precise Enumerative Methods. 197 
(10) Conclusions Regarding the Nature and Cause of the Trypanosome Cycle. 
The true explanation of this phenomenon must be of extreme importance, 
not only as regards the treatment of this disease, but also, we think, with 
regard to the problems of immunity in general. | 
Before stating our views we cannot do better than quote the following 
extract from the Sleeping Sickness Bulletin, 1909, No. 12, p. 485 :— 
“Des Causes des Crises Trypanolytiques et des Rechutes qui les suivent. 
A. MAssaGLia. ‘Comptes Rendus de l Académie des Sciences,’ Octobre, 
1907. 
“In some species of animals there are no crises. The trypanosomes 
increase in a progressive regular manner. In others the trypanosomes, after 
an increase, suddenly diminish to such an extent sometimes that they cannot 
be found in the blood. They soon reappear. Massaglia endeavoured to find 
out the cause of the crisis and the subsequent relapses. . . . Conclusions: 
Trypanolytic crises are due to the formation of anti-bodies in the blood. 
A few parasites escape destruction, because they become used or habituated 
to the action of these anti-bodies. These are the parasites which cause the 
relapses. Since the trypanosomes become more and more used to the anti- 
bodies the subsequent crises become less marked. . . . Thiroux’s suggestion 
of a balance between anti-bodies and parasites is an interesting one and has 
some facts in its support. It would serve to explain the cause of real or 
apparent cures mentioned in Bulletin No. 5, pp. 193 and 195.” 
Here it is clear that Massaglia has observed and has tried to explain the 
occurrence of these natural rises and falls of trypanosomes. Our opinions 
on the subject are as follows :— 
G) Zhe Cycle is not Due to an Unconditional Cyclical Development of the 
Parasites as 1s the Case in Malarial Fever.—If it were so then one would expect 
the cycle to be more regular, and one would not expect its time to be altered by 
vaccine injections. The time between the rises varies not only in the same 
individual, but in different animals. This would appear to suggest that the 
cycle is not due to a definite parasitic development as in malaria, but is 
merely a question of a struggle between the defensive powers of the infected 
body and the aggressive powers of the trypanosomes. 
The more susceptible the animal the shorter is the period between the 
rises as seen in the case of rats, in which the cycle is almost lost. Massaghia 
evidently failed to observe the slight remissions in the rat. 
