IMMUNITY FROM CONTAGIOUS DISEASES. 
63 
ON A NEW METHOD OF PRODUCING IMMUNITY FROM 
CONTAGIOUS DISEASES. 
r D. E. Salmon, D.V.M. and Theobald Smith, M.D. From the Pro- 
ceedings of the Biological Society of Washington, Vol. Ill, 1884-86 
More than four years ago* one of us, in the study of the sub- 
et of insnsceptibity to contagions diseases, reached the con- 
nsion that, in those diseases in which one attack protects from 
e effects of the contagion in the future, the germs of such mal- 
ies were only able to multiply in the body of the individual at- 
sked because of a poisonous principle or substance which was 
oduced during the multiplication of those germs. And also 
it, after being exposed for a certain time to the influence of 
is poison, the animal bioplasm was no longer sufficiently af- 
Jted by it to produce that profound depression and modification 
the vital activity which alone allowed the growth of the path- 
enic germs and the consequent development of the processes 
ft disease. After several series of experiments, made at that 
le with only negative results, it became necessary to suspend 
i ;se investigations until points connected with them, and which 
ie tllen obscure, should be cleared up, and until it should be¬ 
ne possible to repeat the experiments under more favorable 
iditions. Our expectations in regard to this important suh- 
t have at last been realized by the results of experiments re- 
itly made in the laboratory of the Bureau of Animal Industry. 
The bacterium, which we have lately discovered and which we 
ieve to be the cause of swine plague, is killed in liquid cul- 
jes by an exposure to 58° C. for about ten minutes. 
I This method of destroying the bacterium in liquid cultures was 
orted to in studying the effects on pigeons of the chemical 
ducts (ptomaines ?) formed by the bacteria in their vegetative 
;e, and which are probably dissolved in the culture liquid, 
i heated cultures used in these experiments were always 
ed by inoculating fresh tubes therefrom, and, if no growth fol- 
ed this inoculation, the death of the microbes was considered 
iblished. 
^Department of Agriculture, Annual Report, 1881-’82, pp. 290-295, 
