ON A NEW METHOD OF PRODUCING IMMUNITY 

 FROM CONTAGIOUS DISEASES. 



BY D. E. SALMON, D. V. M., AND THEOBALD SMITH, M. D. 



(Read February 20, 1886.) 



More than four years ago * one of us, in the study of the sub 

 ject of insusceptibility to contagious diseases, reached the con 

 clusion that, in those diseases in which one attack protects .from 

 the effects of the contagion in the future, the germs of such mal 

 adies were only able to multiply in the body of the individual at 

 tacked because of a poisonous principle or substance which was 

 produced during the multiplication of those germs. And also 

 that, after being exposed for a certain time to the influence of 

 this poison, the animal bioplasm was no longer sufficiently af 

 fected by it to produce that profound depression and modification 

 of the vital activity which alone allowed the growth of the path 

 ogenic germs and the consequent development of the processes 

 of disease. After several -series of experiments, made at that 

 time with only negative results, it became necessary to suspend 

 these investigations until points connected with them, and which 

 were then obscure, should be cleared up, and until it should be 

 come possible to repeat the experiments under more favorable 

 conditions. Our expectations in regard to this important sub 

 ject have at last been realized by the results of experiments re 

 cently made in the laboratory of the Bureau of Animal Industry. 



The bacterium, which we have lately discovered and which we 

 believe to be the cause of swine plague, is killed in liquid cul 

 tures by an exposure to 58 C. for about ten minutes. 



This method of destroying the bacterium in liquid cultures was 

 resorted to in studying the effects on pigeons of the chemical 



* Department of Agriculture, Annual Report, 1881-2, pp. 290-295. 



