PRELIMINARY NOTE 
ON SOME EXPERIMENTS TO DETERMINE THE COMPARATIVE 
EFFICACY OF THE DIFFERENT CONSTITUENTS OF 
HAFFKINE'S PLAGUE PROPHYLACTIC* 
By C. BALFOUR STEWART, M.A., M.B. Camb. 
The following short note gives the results of experiments done at the Plague Research 
Laboratory, Bombay, between February and May, 1899. The full account has been sent in to 
Government, and will appear in due course. 
A number of Rabbits were inoculated with increasing doses of a young culture of living 
plague in broth, and the somewhat unexpected result was found that the Rabbits which received 
the larger doses showed the smaller mortality. I thought it possible that during the growth 
in broth the latter had acquired sufficient prophylactic properties to render the animal immune to 
the microbes contained in the broth culture injected. 
To see whether the prophylactic property lay in the broth altered during the growth of 
the microbe or in the sediment, several sets of experiments were done in which the broth was 
filtered through a porcelain filter. The sediment of a certain quantity of living plague culture 
was found to be more virulent than the same quantity of broth culture unfiltered when injected 
into Rabbits. 
Some Rabbits were inoculated with the filtrate alone, others with the sterilized sediment 
alone, and immediately afterwards injected with a suspension of living plague from an agar tube. 
The result seemed to show that both the filtrate and the sterilized sediment possessed prophylactic 
properties. 
Immunity seems to be conferred even when the animal is inoculated with the pro- 
phylactic immediately before the injection of plague. 
In testing the virulence of a plague culture, it is evidently important to use only a very 
young broth culture or an agar culture. 
* From the Plague Research Laboratory, Bombay. 
