36 THOMPSON YATES AND JOHNSTON LABORATORIES REPORT 
IV. MORPHOLOGICAL CHARACTERISTICS OF THE HUMAN AND 
HORSE TRYPANOSOME FOUND IN THE GAMBIA 
We propose to give here short descriptions ot the microscopical appearances 
of the human and horse trypanosomes as they are seen in the peripheral blood of 
their respective hosts and in experimentally infected tame rats. 
We reserve a more detailed account of these parasites and a description of 
their appearances in various other animals inoculated for a future report. 
The description or the morphological characteristics ot a pathogenic trypano- 
some presents at the outset great difficulties; so varied are the forms seen, so minute 
are the differences distinguishing one form from another, and so many are the 
intermediate stages between two contrasted forms in any infected animal, that it 
requires some time and study before the characteristic adult form of parasite can be 
finally determined. 
Though we could detect no constant morphological differences between the 
human and the horse parasite — more especially was this the case in inoculated 
animals — still the parasites usually seen in the blood ot horses, examined in the early 
stage of their infection, presented marked differences in size and appearance from 
the parasite usually seen in the blood of the infected natives. 
1 he Human Trypanosome. — Plate I, fig. i, represents this parasite as usually 
seen in the native. 
In stained preparations its length, including the flagellum, averages 20«. Its width 
is i-8 i* to 2 fx. The distance from micronucleus to the centre of the macronucleus is 
<; - 9 m. The distance from the micronucleus to the tip of the posterior end of the body 
was found to vary, as a rule it measured 1*6 m, but parasites were often seen in which 
this distance was only 0*5 
This trypanosome, as seen in the native and quadroon cases, presented no 
features morphologically differentiating it from the one described by one of us in 1901, 
as occuring in the blood ot a European and a native child in Gambia, and named 
T. gambiense. 
The Horse Trypanosome. — The parasite seen in Senegambian horses was never 
encountered in any great numbers in the peripheral blood during the early stages ot 
the infection. The blood of one horse, Case V, in which the disease proved fatal, 
never contained many parasites. 
Plate I, fig. 6, represents the trypanosome as seen in the early stages of 
infection of the horse. The parasite is a very small organism, rather tadpole-shaped. 
