MECHANISM OF INFECTION 81 



(b) The existence in the organism of chemical affinities for 

 these bacterial products. 



2. Infection or contagion is brought about by the pene- 

 tration of bacteria or colloidal bacterial products across 

 the mucous membranes of the digestive or respiratory 

 apparatus or by means of intra- or hypodermic inoculations. 



3. Incubation in infection is the time necessary for a 

 bacterium with the products of its secretion or bacteriolysis 

 to adapt itself to its medium and to cause in the organism 

 the formation of specific antibodies in excess. 



4. The preexistence of antibodies in certain organisms for 

 certain bacteria can be explained: 



(a) By heredity, and 



(b) By individual spontaneous vaccinations. 



5. The formation of normal antibodies, or in other words, 

 specific affinities, when they do not preexist, can be explained 

 by the infection itself, or, in other words, by the penetration 

 into the interior of the organism of colloidal bacterial pro- 

 ducts in immunizing doses during the incubation period. 

 In this case the bacterium itself will create the affinity. 



6. Every bacterium which can adapt itself to an animal 

 medium, that is to say, which can digest and assimilate 

 certain animal substances in the colloidal state, can become 

 pathogenic for that animal. 



7. The state of resistance on ingest ion to bacteria when 

 ingested is due to the complete digestibility of all bacteria 

 and all their products by gastro-intestinal digestion. 



The state of resistance on inoculation results from the 

 absolute inability of the bacteria to be nourished in the 

 animal medium. 



8. Active immunity is a state of resistance of the organism 

 to a certain dose of infecting bacteria which is rapidly and 

 easily digestible. It will be complicated by an anaphy- 

 lactic hypersensitiveness whenever the compound of antigen , 

 with antibody in excess is insoluble, and therefore, more 

 or less difficult to digest. There will be no hypersensitive- 

 ness when this compound is soluble and neutral. 



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