1910.] Treatment of Animals infected with Trypanosomes. 231 
incubation was allowed to take place. Three rats were treated with vaccine, 
and three were kept as controls. 
Treated with Vaccine. Controls Untreated. 
Rat 42 ......... Lived 21 days. at LAr. een Lived 12 days. 
at 43) oii. .s0. Bs oes Raibeloe iccetine i Oe 
1A ae Ea aaah Rat liso Me TOA ke 
Here an interesting point can be noted. It will be seen that Rat 42 treated 
with vaccine lived 21 days, whereas Rats 43 and 44, also treated with vaccine, 
only lived 9 and 11 days respectively. | 
We would suggest that this is explained by the fact that the vaccine 
in the case of Rat 42 was administered in two doses of 10,000,000, with 
an interval of one day between the doses, whereas Rats 43 and 44 received 
two doses each of 12,000,000, no interval of a day being allowed. 
In the case of Rat 42, we have the life prolonged in a remarkable 
manner. The longest life of our three controls was 12 days, and the 
average life of 22 untreated animals, infected with the same strain, was 
11:3 days, where the longest life recorded was 18 days (Fantham and 
Thomson). 
When a vaccine is administered during a natural rise of trypanosomes we 
have on the following day a rise in the number of trypanosomes in the 
peripheral blood, and this represents 4 negative phase. A second dose of 
vaccine ought therefore not to be administered at this period, as was done 
in Rats 43 and 44, or more harm than good may be accomplished. On the 
other hand, if we allow a day to intervene, as was done in Rat 42, we give 
the vaccine at a favourable period, the negative phase having passed off. 
We admit, however, that much more extensive experiments will require 
to be undertaken, and would suggest that failure in vaccine treatment in 
trypanosomiasis until the present time has been caused by the vaccine 
being administered at the wrong time. Probably the best time to administer 
a vaccine is when the trypanosomes are low in numbers in the peripheral 
blood, and a second dose ought not to be administered until the negative 
phase has passed off (see R. Ross and D. Thomson).* 
We have said that the trypanosomes increased in numbers in the 
peripheral blood after a subcutaneous injection of vaccine. This is in all 
probability to be explained by the hypothesis of Dr. H. C. Ross, who holds 
that the extracts of dead tissues stimulate cell division.t 
* “Roy. Soe. Proc.,’ B, vol. 83, pp. 187—205. 
+ ‘Brit. Med. Journ.,’ June 11, 1910. 
