4° 7 
X. 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 dcs Crises Trypanolytic et des Rechutes qui les suivent. 
• A MASSAGLIA. “ Comptes Rendus de l’Academie 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. . . • Thirouxs suggestion o 
‘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 fa 
trypanosomes. Our opinions on the subject are as follows. 
(i) The cycle is not due to an unconditional cyclical development 
of the parasites as is the case in malarial fever . If it were sot en 
one would expect the cycle to be more regular, and one won 
expect its time to be altered by vaccine injections- ie im 
between the rises varies not only in the same in im ua , 
different animals. This would appear to suggest that the cycle 1 
not due to a definite parasitic development as in ma aria, 
