NEW METHOD OF PREVENTING CONTAGION. 33 



already at hand. The internal organs were not macroscopically 

 altered, excepting the spleen of No. 8, which was enlarged and 

 dark. The presence of the bacterium of swine plague in the blood 

 from the heart was demonstrated by liquid cultures, which, inocu- 

 lated with a minimum quantity of blood, were turbid with this 

 specific microbe on the following day. 



The conclusions to be drawn from this experiment we believe 

 are of superlative importance to a correct understanding of the 

 phenomena of contagious diseases, and the methods by which 

 these diseases are to be combated. They probably apply to all 

 bacterial plagues of men and animals in which one attack confers 

 immunity from the effects of that particular virus in the future. 

 These conclusions are : 



1. Immunity is the result of the exposure of the bioplasm of 

 the animal body to the chemical products of the growth of the 

 specific microbes which constitute the virus of contagious fevers. 



2. These particular chemical products are produced by the 

 growth of the microbes in suitable culture liquids in the labora- 

 tory, as well as in the liquids and tissues of the body. 



3. Immunity may be produced by introducing into the animal 

 body such chemical products that have been produced in the 

 laboratory. 



