287 
Rats became infected although trypanosomes were not seen in 
the animal from which the blood was taken for over a month both 
before and after the subinoculation. They became infected even 
although large doses of Atoxyl or of Atoxyl and Mercury had been 
given to the infecting animal only a day previously. Blood taken 
during a rise in temperature was often infective; but blood taken 
while the temperature was no higher than usual, and at a time neither 
preceding nor following a rise, was also infective; blood taken 
during the customary ante-mortem fall of temperature was infective 
in four of these thirteen experiments, although trypanosomes were 
absent from it. . . • 4.1, 
The chief interest in these successful subinoculations lies in t e 
fact that the incubation period was greatly lengthened, whie t 
course of the disease, once the parasites appeared in the blood, was 
normal, and the rats died about three days later.In six ° ^ 
thirteen subinoculations the incubation period was over tee y 
in three over twenty, the longest was twenty-six days; only once, 
and then in blood taken from a dying animal, was the incu a 10 
short as four days. Although other explanations suggest t^emselv . 
these observations seem to be in harmony with our e 1 
recurrences in apparently-cured, trypanosome-infecte anim 
due to the production and persistence of some resistant 
form of the parasite, and not merely to the acquirement of 
therapeutic resistant ’ properties by it. 
