272 BACTERIOLOGY 



death of the bacteria to purely physical conditions; believing 

 that their exposure to blood-serum having an osmotic tension 

 different from the fluids in which they had been growing 

 resulted in disturbances of the bacterial protoplasm that 

 were inconsistent with bacterial life. 



By the observations of Behring 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 investigators 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 or of diphtheria bacilli, 

 entirely free from the germs themselves, be injected into 

 susceptible animals in minute sublethal doses the animals 

 presently acquired immunity from both poisons and 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 neu- 

 tralized, i. e., the serum of the animal acted as an antedote 

 which rendered the bacteria 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 immunity seen in 



