399 
V CORRELATION BETWEEN THE TRYPANOSOME CYCLE 
AND THE BEHAVIOUR OF THE LEUCOCYTES 
Previous to April 23 we made several leucocyte counts with the 
Thoma-Zeiss apparatus, but were unable to find anything definite. 
It was only when we made counts daily at the same hour that we 
were able to find a definite leucocyte change corresponding to the 
parasitic cycle. 
We counted the leucocytes by means of the thick film as referred 
to in our paper on malaria, and were astonished at the remarkable 
variations. We found no such variations by our method in normal 
persons. Simultaneous examination of thin blood films also showed 
that a remarkable leucocytic variation did take place, corresponding 
to each rise of trypanosomes. 
Daily differential counts were also made in thin films stained 
with Giemsa, in which we distinguished only between mononuclears 
and the so-called polymorphonuclears. In these we never counte 
less than from 300 to 500 leucocytes to ensure greater accuracy. 
We thus estimated daily the total leucocytes and the total numbers 
of polymorphs and mononuclears per cubic millimetre of blood, as 
shown in the chart and table. . 
From April 23 till May 20 it is clearly seen that coincident with 
each rise in the number of trypanosomes there is a marked increase 
in the total leucocytes, and this increase is due more to mononuclears 
than to polymorphonuclears. 
When the trypanosomes begin to increase in number the 
leucocytes increase also, more especially the mononuclears. When 
the trypanosomes have reached their height there may be a a in 
the number of leucocytes, but this is followed by a still higher rise 
during the fall of the trypanosomes. The leucocytes would seem 
to reach their highest numbers on about the third day after the 
height of the parasitic cycle. They then decrease rapidly for about 
three days to normal or much lower. When this occurs the 
trypanosomes again commence to multiply, and the leucocytes again 
increase also, so that we have both a parasitic and a corresponding 
leucocytic cycle. , 
We did not attempt to differentiate between large mononuclears 
and lymphocytes, but it seemed to us that both took part in the 
total mononuclear increase. We further observed that during an 
