It would seem, therefore, that the explanation may be reduced 
to some of the following causes, all of which may come into play. 
(i) The increase of trypanosomes is due to their active 
multiplication , the rate of multiplication depending on the following 
conditions : — 
( a ) The liberation of a reproductive stimulant from the dead 
trypanosomes of the previous fall. 
( b ) The small number of leucocytes, especially mononuclears. 
(c) The habituation of the trypanosomes to their anti-bodies. 
( d ) The absence or the diminution of anti-bodies to the 
trypanosomes. 
(ii) The decrease of trypanosomes is due to their rapid death and 
to a cessation of multiplication , probably depending on the 
following conditions: — 
(a) The presence of anti-bodies in the serum. 
(b) The large increase of leucocytes, especially mononuclears. 
(iii) The trypanosomes remaining between the rises are resistant 
forms , and tend to become spherical, especially in the internal 
organs. (Vide H. B. Fantham.*) 
These resistant spherical forms also occur alter atoxyl treatment 
(Moore and Breinl). 
N.B.—The reference to the virulence of this trypanosome and 
to the cycle in rats and guinea-pigs is taken from the papei on 
enumerative studies in rats, guinea-pigs, and rabbits by H. B. 
Fantham and J. G. Thomson, t 
The virulence of this strain was also noticed by L. E. W. Bevan 
and Malcolm Macgregor (‘ Journal of Comparative Pathology and 
Therapeutics,’ June, 1910), who inoculated animals from our 
patient before he left N.E. Rhodesia. 
* Ann. Trop. Med. and Parasit., Vol. IV, pp- 
I.XXXIII. pp. 212-227. 
t Ann. Trop. Med. and Parasit., Vol. IV, pp. 
i.XXXIII, pp. 2ofi-2tl. 
465-485; also Proc; Roy. Soc., B, Vol. 
417-463 ; also Proc. Roy. Soc., B, Vol. 
