422 BACTERIOLOGY. 



the immunity that has been produced artificially by vac- 

 cination, exists by virtue of some bacterial product that 

 has been retained or deposited in the tissues of those 

 animals, and that this product by its presence prevents 

 the development of the same organisms if they should 

 subsequently gain access to the body. 



Bearing upon this view the experiments of Sirotinin, 1 

 made with cultures of various pathogenic bacteria, dem- 

 onstrated that, in so far as culture experiments were con- 

 cerned, the only substances produced by growing bacteria 

 that could be in any way inimical to their further devel- 

 opment were substances that gave rise to alterations in 

 the reaction of the medium in which they were develop- 

 ing, i. e.j acids or alkalies produced by the bacteria 

 themselves. So long as the organisms were not actually 

 dead from exposure to these substances, correction of the 

 abnormal reaction was followed by further development 

 of the organisms. Sirotinin also states that materials 

 containing the products of growth of bacteria, so long as 

 they are maintained at a neutral or only slightly alka- 

 line reaction, serve very well as media upon which to 

 cultivate again the same organism that produced them, 

 providing the nutritive elements have not been entirely 

 exhausted. He remarks that, if in such a concentrated 

 form as we find the life products of bacteria in the 

 medium in which they are growing, no inhibitory com- 

 pounds beyond acids and alkalies are to be detected, it is 

 hardly probable that they are produced in the tissues of 

 the living animal, and retained there, to a degree suffi- 

 cient to prevent the growth of bacteria that may subse- 

 quently gain entrance to these tissues, after the disap- 



i Zeitsch. fur Hygiene, 1888, Bd. iv. 



