the stages of the infection, m the non-pathogenetic fonn 
T. lewisi all the stages of the life cycle may be present and 
represented by different parasites which arc found in the blood at the 
same time. This difference is perhaps what might have been 
expected Such forms as T . lewisi are usually present in the animais 
they inhabit m large numbers for weeks, or even months; whereas 
among the pathogenetic varieties the parasites are numerous in the 
blood for only relatively short periods, the phases of the life cycle 
eing here apparently adapted to the varying conditions of the host 
n t IS way we find that the parasites in such forms either 
multiply without limit, and by their action rapidly kill the host, or thev 
periodically disappear from the altered blood in the form of law 
\\t' ^ reappear, it may be, after a very considerable time. 
We have referred, in dealing with T. gambiense and 
Z-. egutperdu^, to the fact that we have been quite unable to make 
ft, ° ^ arbitrary distinction which has come into vogue since 
„ j ‘‘^chaudinn between the so-called males, females, 
and any different forms. These seem to us to be either mere 
f-vam ?i. morphological distinction is obtained, 
P s at ave been talcen from different parts of the life cycle. 
thp cti ,1 in relation to this matter have been enforced by 
biolocn' ^^isi. Moreover, the terms male and female have, 
vIetTe? r T obvious reference to fivo 
type in ref ^ conjugate, or gametes, and to use terms of this 
characters varieties of size, or to the morphological 
enniueation h phases in a life cycle where no ordinaiy 
