333 
at a time when trypanosomes are decreasing in the 
blood, the majority of trypanosomes are disintegrated 
into a mass of debris, but some become rounded and 
encysted (Moore and Breinl). 
Latent Forms .—During the course of an infection 
when trypanosomes are decreasing in the blood, Moore, 
and Breinl describe forms found at first in the lungs 
and somewhat later in the spleen and bone marrow 
(and in small numbers in the blood), which they call 
latent forms. They are minute forms consisting of 
a nucleus with an intranuclear body (centrosome) and 
a vesicle, the whole lying in a thin film of protoplasm. 
These exist, then, in the organs (a few also in the blood) 
Fig . 106 
when trypanosomes are absent from the blood, and 
some of these give rise again to young, and then full- 
grown trypanosomes which multiply by longitudinal 
division as described above. Trypanosomes thus 
appear to have, at least in the case of a rat infected 
with T. gambiense , a regular cycle in the body. It is 
possible that these minute forms are the source of 
infection in blood which, although filtered, is still 
infective. 
Involution Forms .—These are the amoeboid 
forms of some observers. They have lost their 
flagellum and are found under various unfavourable 
conditions, e.g., in the blood of animals under treatment 
with atoxyl, etc., also in the spleen (Fig. 106), or in 
blood that has been heated to 40° for one hour, or 
in -post-mortem blood. 
