ANTI-TOXIC AND ANTI-BACTERIAL IMMUNITY. 89 



in the body exist. Conditions favorable to the liberation of 

 toxins have up to the present time been produced for a few 

 bacterial species, so that most bacteria only liberate their 

 toxin in the tissues of the body invaded. As a result of 

 immunization to two widely different substances, toxin and 

 bacterial cells, two different classes of immune sera have been 

 manufactured. Of these two classes, the anti-toxic sera neutralize 

 certain morbific bacterial products, while the ant i -bacterial sera 

 destroy the bacterial cells. It is not to be inferred from this 

 that the same serum may not be both anti-toxic and anti- 

 bacterial, for diphtheria toxin and cells, for example, may be 

 used in immunization. Under such conditions the blood serum 

 obtained will have both anti-toxic and anti-bacterial value. 



Acquired anti-toxic immunity is an immunity due to a neu- 

 tralization of toxin by a specific anti-toxin. The substance that 

 is formed as a result of the combination of toxin and anti-toxin 

 acts like a harmless and stable compound. Ehrlich, basing his 

 observations on studies of the union of toxin and anti-toxin, 

 classes the anti-toxic bodies formed with the anti-bodies of the 

 first order, that is, the labile susbtance or complement takes no 

 part in the reaction. In natural immunity to certain toxins the 

 presence of specific anti -bodies cannot be demonstrated and un- 

 der these conditions immunity is rather a non-susceptibility of 

 the cells to the toxin. Metchnikoff has shown that tetanus toxin 

 circulates freely in the blood of naturally immune animals. In 

 certain other cases of natural immunity toxin combines with cells 

 that are of little importance to the body or which are but little 

 affected by the particular toxin. Acquired anti-toxic immunity 

 thus differs from natural immunity in the formation of immune 

 bodies. These immune bodies are found in the body fluids, 

 especially the blood serum and can be injected into other animals 

 or individuals and in this way confer upon them a passive 

 immunity. 



Acquired anti-bacterial immunity is an immunity depend- 

 ent upon the rapid destruction of bacteria. The process 

 is one of solution or lysis. The anti-bodies which produce lysis 

 belong to Ehrlich's third order of immune bodies, that is, com- 

 plement, which is easily destroyed by age, heat, etc., is necessary 

 to bring about the solution of bacteria. Natural immunity to 



