MECHANISM OF INFECTION 75 



bacilli only rarely become pathogenic, because the digestion 

 of the bacterial body and the products of bacteriolysis ought 

 to be complete in the intestine. 



A true and lasting immunity would consist in rendering 

 the organism refractory to anaphylactic hypersusceptibility; 

 that is to say, to render the organism capable of completely 

 digesting bacteria or products of bacteriolysis in the stomach 

 and intestines so as to hinder these products from penetrat- 

 ing in- the form of specific colloids into the blood as well as 

 into the cells of the mucosa and of the intestinal glands. 



Some experiments on mouse typhoid permit the hope that 

 this will be not impossible of accomplishment. One may 

 demonstrate that if some or rather some dozens of bacteria 

 are necessary to infect an animal by subcutaneous injection, 

 several thousand times as many are necessary to infect an 

 animal by the ingestion of a pure culture and several millions 

 if this pure culture is mixed with another substance of 

 whatever nature. 



If then, after having determined the minimum lethal 

 dose by ingestion of a pure culture, the animal is treated 

 during and after by hypodermic injections of sodium caco- 

 dylate or calcium glycerophosphate in convenient doses, it 

 is found that the animal thus treated resists doses which 

 are very fatal for controls. It is also found that animals 

 treated in this way are not vaccinated and have no specific 

 antibodies in their blood which proves that the bacteria 

 or their antigens have not been able to penetrate into the 

 interior and that they have been very probably digested in 

 the stomach and intestines, or perhaps evacuated without 

 having- been attacked by digestion. 



From another aspect it is possible to determine by a 

 series of tests that the same paratyphoid pathogenic for 

 mice and completely harmless in the beginning for Mus 

 Decumanus and Mus Rattus can little by little become 

 more and more pathogenic for these species by ingestion 

 as a result of a series of alternate passages: (1) In vitro 

 in a broth culture prepared with the flesh of the animals of 

 this species; and (2) in collodion sacs inclosed for twenty- 

 four hours in the peritoneal cavity of these animals. Cul- 



