19 
of trypanosome blood they found in the peritoneum several engaged 
in development. They think that as soon as development is perfected 
in the peritoneum the parasite disappears from the peritoneal fluid 
into the blood. They give some weight to the fact that in one case of 
intravenous injection of parasites multiplication did not occur until 
the flfth day. Laveran and Mesnil state that there is less multiplica- 
tion in the blood than in the peritoneum. 
Our observations speak for the blood as the principal seat of devel- 
opment. On examination of the peritoneal fluid at varying times 
after injection we did not And division forms, nor did we And the 
flrst existence of parasites in the'tail blood accompanied by division 
forms. The most reasonable explanation seems to be that if a large 
amount (0.75 c. c.) of heavily infected blood be injected into the 
peritoneal cavity, the small young forms and the long slender adults 
pass at once by the lymphatics into the general blood stream in suffi- 
cient numbers to be detected in cover-slip preparations within twenty- 
four hours or even within twenty-minutes, but the rosettes and other 
large division forms which are injected into the i)eritoneal cavity are 
prevented by their size from passage through the lymph channels 
and remain behind in the peritoneal cavity until their division is 
complete, when the young then pass through the lymph passages into 
the blood, leaving the peritoneum permanently free from parasites. 
Daily examination of the blood for one to two days after the first 
appearance of parasites in the tail blood shows at most only a very 
gradual increase in the number of parasites present, but suddenly 
there comes an enormous swarming of the blood Avith t)arasites, and 
the presence of rosettes and other division forms indicate that multi- 
plication is going on in. the blood. The slide from which the micro- 
photographs (PL III, figs. 11, 12) were made shoAvs at least two dozen 
rosettes and was taken from the rat on the second day after the first 
appearance of parasites in the tail blood. It is not unusual to find 
parasites in the proportion of 1:2 red blood cells. Exceptional 
instances are met with in which the blood corpuscles are outnumbered 
by the* trypanosomes. The duration of the period of multiplication 
is often no more than twelve to twenty-four hours. By the fourth 
day after the first entrance of parasites into the blood the height of 
infection has been reached. Rabinowitsch and Kempner found no 
division forms in the blood on the fourth day after the first appear- 
ance of parasites in the tail blood. 
By subcutaneous inoculation . — Blood infection occurs by this 
form of injection a little later than hy intraperitoneal inoculation. 
The shortest time in our cases between inoculation and the appear- 
ance of parasites in the blood was three days. Multiplication pro- 
ceeded in the blood until it swarmed with myriads of parasites. This 
would seem to be additional evidence to the superiority of the blood 
over the peritoneal fluid as a nutritive medium for the development 
of the parasites, for in cases where the parasites had advantage of 
