216 Immunity in Canine Piroplasmosis 
results may be briefly summarized as follows : on mixing the blood of 
recovered dogs with virulent blood and injecting the mixture into 
healthy dogs the latter did not become infected. They attributed this 
result to the existence in the immune serum of a substance which they 
thought was capable of destroying the parasites. They stated that the 
germicidal substance was greatly increased in amount in the serum of 
hyper-immunized dogs, that the serum of recovered animals had marked 
protective properties when injected in large doses 24—48 hours before 
inoculation with virulent blood, and that the serum of hyper-immune 
animals was much more active in this respect since 3 to 5 c.c. sufficed to 
protect susceptible dogs. They found that immune serum still exerted 
a protective action after having been heated to 56—57° C. Infected red 
blood corpuscles, exposed to the action of immune serum, and afterwards 
washed and injected, also conferred immunity. Passive immunity only 
lasted a short time, for animals upon which passive immunity had been 
conferred could be infected after periods varying between 11 and 35 
days. Finally they stated that immune serum was curative if injected 
before the parasites appeared in the blood of inoculated dogs. 
The results of Robertson (1906) at the Cape are in marked contrast 
to those of Nocard and Motas in France. Robertson found that the 
parasites remained fully virulent for a considerable time in the blood of 
“recovered” dogs. When the blood of the two “salted” dogs he used 
had ceased to be infective , he tested it for immunizing power on fresh 
dogs. He injected doses of 20 c.c. of recovered blood into the dogs he 
desired to protect and then injected 3 c.c. of virulent blood. The results 
wei-e uniformly negative. 
When Robertson sought to hyper-immunize salted dog “11,” by 
injecting 20 c.c. of virulent blood, the dog developed a mild attack of 
piroplasmosis (temperature 104 n F. on the 5th day; parasites in the 
blood for over 14 days). 
Salted dog “ 45 ” was injected 6 times subcutaneously at intervals of 
3 weeks with virulent blood, the doses of blood amounting respectively 
to 10 c.c., 25 c.c., 50 c.c., 250 c.c., 500 c.c. and 1000 c.c. This dog reacted 
to each injection but did not suffer ill-effects from the disease although 
the parasites reappeared in its blood and persisted therein for 9 days. 
Twenty-seven daj’s after the last injection of virulent blood the dog was 
bled and 500 c.c. of its serum were collected. The serum was tested 16 
hours later as follows : 
Nine dogs were treated with the immune serum : 2 received 5 c.c. 
each and 7 received 10 c.c. each injected subcutaneously. In accordance 
