562 BACTERIOLOGY. 



ing resulted in disturbances of the bacterial protoplasm 

 that were inconsistent with bacterial life. 



By the observations of Behriug and Kitasato and of 

 Roux and Yersin entirely new light was thrown upon 

 the subjects of infection and immunity and a new field of 

 inquiry was opened. Through the work of these in- 

 vestigators and their pupils upon tetanus and diphtheria 

 it was demonstrated that immunity was, at least in certain 

 diseases, not so much a matter of actually destroying 

 the invading bacteria as of neutralizing their poisons. 



The outcome of these investigations established the 

 fact that if the poisons of tetanus bacilli and of diph- 

 theria bacilli entirely free from the germs themselves 

 be injected into susceptible animals in minute doses the 

 animals presently acquired immunity from the living 

 organisms. Furthermore, that the blood serum of 

 animals thus immunized had the power when transferred 

 directly to normal animals of at once rendering them 

 insusceptible to infection by the living germs, and of 

 equal importance, that if the blood serum of an animal 

 thus immunized be added to the bacteria-free poison of 

 either the tetanus or diphtheria bacillus in a test tube 

 that the poison was neutralized, i. e., the serum of the 

 animal acted as an antedote which rendered the bac- 

 terial poison inert. 



It is obvious therefore that through the injections into 

 the normal animals of non-fatal quantities of the specific 

 bacterial poisons the tissues had been stimulated to react 

 in a manner quite in harmony with the views of 

 Buchner expressed in 1883, to the effect that the im- 

 munity seen in an animal that has recovered from a 

 specific infection is explainable by a " reactive change " 



