218 Immunity in Canine Piroplasmosis 
reason for pursuing the investigations in this direction after the excel¬ 
lent results from drug treatment obtained by Nuttall and Hadwen. 
(b) Authors’ attempts at immunization by inoculations with 
blood containing dead parasites. 
In the experiments about to be described an attempt was made to 
render dogs immune to piroplasmosis by a method which has not been 
attempted hitherto. We sought to render dogs immune by injecting 
them with successive doses of blood containing dead parasites. The 
blood used for immunization was collected from the hearts of dogs killed 
in an advanced stage of the disease so as to ensure the presence of many 
parasites in it. We hoped that this injection of dead parasites into 
the dogs might lead to the formation of protective antibodies in the 
animals. To ensure the death of the parasites the blood was either 
allowed to dry or it was allowed to stand at room temperature after the 
addition of a small amount of citrate and of carbolic acid. 
Only one experiment (Dog 5) was carried out with blood which had 
been dried because it was found difficult to redissolve dried blood com¬ 
pletely and aseptically. 
The fluid blood, used for treatment, was defibrinated and citrate 
was added with the object of preventing the secondary coagulation 
which occasionally takes place. Measured quantities of blood (usually 
10 c.c.) were placed in sterile cotton-plugged test-tubes after which 3 to 5 
drops of 5 % carbolic acid solution were added to each tube. After a 
short time the corpuscles gravitated to the bottom of the tubes. In some 
cases the whole of the fluid in the tubes was shaken up and injected, in 
other cases the supernatant fluid was pipetted off and a concentrated 
suspension of corpuscles was injected. 
The fluid blood, used for treatment, was usually allowed to stand for 
several days before it was injected, for in two cases the parasites survived 
in a virulent state in the weakly carbolized blood for periods of 24 and 
72 hours respectively at room temperature. In all cases the dogs 
received several injections of blood prior to their being subjected to the 
test inoculation with fresh virulent blood. 
The following protocols relate to four dogs which were treated with 
fluid blood and to one dog which was treated with dried blood. All the 
dogs died. Dog 1 showed parasites on the 10th day after inoculation with 
virulent blood but no parasites could be detected in its heart-blood at 
autopsy (partial immunity ?, see p. 222). Dogs 2, 3 and 5 died of piro- 
