484 BACTEEIOLOGY. 



Anti-Infectious Serum. 



The serum of an animal which has ibeen immunized by 

 repeated injections of a soluble toxin, as in the case of diph- 

 theria, possesses antitoxic properties. That is to say, it 

 contains a substance, antitoxin, which in some way neutral- 

 izes or renders inert the soluble poison when introduced 

 into the body. This antitoxic serum should be > sharply dis- 

 tinguished from the antir-infectious serum which results when 

 an animal is immunized by repeated ijijections ofi certain 

 living' or dead bacteria. The defense of the body is carried 

 out either by destroying the soluble poison that' is being 

 made in the body, or by destroying the bacteria themselves. 

 There are, therefore, two distinct agencies at work. 



By repeated injections of dead or living bacteria the 

 cells are taught to take up, or otherwise destroy, the solid 

 invading organisms; The serum of an animal thus immun- 

 ized possesses the property of stimulating' or causing the 

 destruction of bacteria. It may incidentally possess, more 

 or less, antitoxic action. If, for instance, the pest bacillus 

 is injected subcutaneously into the horse the organism is 

 localized at the point of injection and may grow at that 

 point for some time. In so doing, it elaborates poisonous 

 products which now induce the same reaction in the body 

 as if they were injected separately. For the same reason, 

 the blood of a horse immunized with living diphtheria 

 bacilli is antitoxic rather than anti-infectious. 



The anti-infectious serum has been especially studied 

 in connection with cholera, typhoid fever, pest and rouget. 

 It is evident from what has been said that a given organ- 

 ism may give rise to serums entirely distinct in action ac- 

 cording as the soluble poison or the solid cell is injected. 

 Thus, the serum of an animal vaccinated with the living or 

 dead cholei;a. vibrio will protect, in even extremely minute 

 amount, against inoculation with the living germ, but 



