merely a question ot a struggle between die 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. 
.Massaglia evidently failed to observe the slight remissions in the 
rat. 
J lie greater the resistance of the infected animal the longer is 
the cyclical period, as in guinea-pig and man. 
Hy an unconditional cycle ’ we mean one of which the period is 
not affected by the resistance of the host or by therapeutic agents— 
as, for instance, that of Plasmodium. By a ‘conditional cycle' 
we mean one which is so affected—as in the present case. 
(ii) The increase of parasites is due to their sudden and active 
multiplication . — The presence of numerous dividing forms during 
the cyclical rise would seem to support this statement. 
(iii) 7 he multiplication of trypanosomes is extremely rapid—hi 
before stated they seem capable of dividing in man three to four 
times in twenty-four hours. 
In rats the rate of multiplication would seem much greater, as 
many as ten divisions or generations may occur in twenty-four 
hours. 
(iv) 7 he rate of multiplication depends on the suitability of the 
inf cited blood to the parasite . — The blood of rats seems more 
suitable to the parasite than the blood of man and guinea-pigs. 
Also this suitability would appear to vary from time to time in 
t ie same animal. In our case there occurred high and low rises in 
e numbers of trypanosomes. Moreover the three highest rises 
recorded in the chart were followed by the three lowest rises 
recorded. This is a very significant fact. It would appear to 
r a ^ e ^ a * a high rise sets up some reactionary condition. This 
ction, il great, not only causes the decrease of trypanosomes 
Ut CXtends its influence so far as to reduce the next rise. 
de^'l ^ le ™ num ^ er °f P ar asites is not due to the toxins they 
eve op. I n man the num b ers ma y reac h on ]y 2 oo per cubic 
metre of blood and then they diminish, whereas in rats they 
y eaci over 200,000 per cubic millimetre of blood and yet 
i , r * se ’ and the toxins in the latter case must be much more 
abundant than in the former. 
