34 8 
with T. gambiense , this is a striking point and can hardly be an 
oversight. 
3. We ourselves have been unable to find posterior nuclear forms, 
though constantly searched for, in the blood of rats infected with 
the old laboratory strain of T. gambiense. 
4. Posterior nuclear forms exist also, as is well known, in 
T. transvaaliense , and by Liihe these are regarded as developmental 
stages of T. tkeileri. Whether this be so or not, the condition is 
not parallel to the one under discussion, for the differences in 
T. tkeileri are characteristic of all strains of this trypanosome, but 
the forms which we have described in this paper have, we believe, 
never been seen before in any strain of T. gambiense in man or 
animals. 
5. We are aware that parasitic flagellates may exhibit 
morphological variations due to changes in metabolism or to 
differences in environment. However, this Rhodesian strain of 
trypanosome with posterior nucleus was seen in rats infected from 
the patient before he was treated with drugs. At first sight also 
it might appear that the posterior nucleus denoted merely 
approaching division or even assumption of the round form. 
However, wc have seen division of these posterior nuclear forms 
(fig. 12). In any case the peculiar morphological feature exhibited 
by the Rhodesian trypanosome, in the possession of a posterior 
nucleus, has not been recorded before. 
As to the meaning to be attached to these forms, we will consider 
the following main possibilities: — 
( a ) That we are dealing with a ‘ variety ’ or ‘ local race ’ of 
/ . gambiense due to some change of environment. The possibility 
in this case exists of 7 . gambiense having been conveyed by a 
species of Glossina other than Glossina palpalis, which may account 
for the peculiar morphology we record; but it must be added that 
we have no knowledge of any' other trypanosome undergoing 
similar changes owing to such a cause. That it is a ‘laboratory’ 
variation we think is out of the question, as all the known laboratory 
strains of T. gambiense are practically identical in morphology'. 
(b) 1 hat we are dealing with a new' species of trypanosome also 
producing Sleeping Sickness in man. In support of this view there 
is fnstly', the morphology'', which considered alone is strong evidence, 
