3/6 BACTERIOLOGY. 



" learning " of physiological stimuli), and the 

 irritability or disease predisposition is height- 

 ened. This is what happens in rheumatism, 

 catarrh, influenza, pneumonia and diphtheria. 

 Or it may be that the resistance to a discharge 

 of energy is increased as the result of adapta- 

 tion, and thus an habituat l *on to the stimulus 

 makes its appearance, so that the same stimulus 

 is no longer able or is less easily able to cross 

 the physiological threshold and cause reaction. 

 The degree of resistance not only varies greatly 

 in different diseases, but even in different in- 

 dividuals towards the same disease. There are 

 some men who become ill through vaccination, 

 and others who gain through vaccination no 

 immunity whatever against small-pox. Only 

 a slight immunity is acquired as the result of 

 an attack in some diseases, as, for instance, in 

 tetanus and cholera. 



A part only of the " specific " curative in- 

 oculations possibly, for example, Pasteur's in- 

 oculation against rabies are to be conceived 

 as anticipatory protective inoculations. The 

 action of the anti-substances in serum therapy, 

 especiall} 7 , shows that some of these cures by 

 injection have nothing to do with protective 

 inoculation and depend simply upon the effect 

 of one active body, the antitoxin or the prc- 

 teid of the serum, on another active body, the 



