404 
The later vaccines which we commenced to use from May 17 
were simply the blood of rats, taken when the trypanosomes were 
very numerous. They consisted of dead trypanosomes, red cells, 
leucocytes, and serum. The injection of these vaccines produced 
no local reaction, even in doses of 100,000,000 trypanosomes; nor 
were we able to detect any definite temperature reaction. 
We are inclined to think that the chief result of these injections 
of dead trypanosomes was a stimulation of the reproductive powers 
of the living trypanosomes. This point, however, requires further 
elucidation. We found that after an injection of our vaccine, the 
next trypanosome rise usually occurred before it was naturally due. 
On April 9, 9,000,000 dead trypanosomes were injected; the 
next trypanosome rise reached its height on the seventh day. 
20,000,000 were again injected on April 13, and the following rise 
was completed on the sixth day. 40,000,000 were then injected 
and the next rise was completed on the fifth day. 
I he patient’s trypanosomes, also, which were rising to 
successively smaller heights, continued to diminish further in 
number, after two more injections of 10,000,000 dead trypanosomes 
on April 23 and 25. On April 28, however, an injection of 
10,000,000 was given when the trypanosomes were increasing, and 
that rise was the highest recorded. This treatment was then stopped 
for some time. 
It seems that the effect of these so-called vaccines, if injected 
immediately after the natural fall of the parasites, is a reproductive 
stimulation of the parasites, causing the next rise to occur sooner 
than was natural; and this premature rise tends to be less high than 
it probably should have been in the natural course of events. 
If, however, the vaccine be injected during the natural rise of 
the trypanosomes, it stimulates their reproduction, causing a very 
high and lapicl rise, and the subsequent fall is also very sudden. 
We confirmed these surmises later. On May 17 an injection of 
30,000,000 dead trypanosomes was given, with the result that the 
following rise was completed on the sixth day. 
Another injection of 50,000,000 on May 30 was followed by a 
nse at the normal time. A large dose of 100,000,000, injected on 
une 4, however, scarcely allowed the parasites any time to diminish, 
so that they completed their next rise on the fifth day, followed by 
