468 IMMUNITY. 



chemical substances separated from filtered bacterial cul- 

 tures, though these substances are generally in a more or 

 less impure condition. Hankin was the first to obtain 

 this result by means of an albumose separated from 

 anthrax cultures. 



Though, as already stated, none of these methods can 

 be used directly as curative agents, seeing that they imply 

 previous treatment before exposure to infection, yet they 

 supply the means of developing a very high degree of 

 immunity, which is the first stage in the production of an 

 active curative serum. 



Active Immunity by Feeding. Ehrlich found that mice 

 could be gradually immunised against ricin and abrin by 

 feeding them with increasing quantities of these substances 

 (vide p. 1 60). In the course of some weeks' treatment in 

 this way the 'resulting immunity was of so high a degree 

 that the animals could tolerate 400 times the originally 

 fatal dose by subcutaneous inoculation. Fraser also found 

 in the case of snake poison that rabbits could be immunised, 

 by feeding with the poisons, against several times the lethal 

 dose of venom injected into the tissues. 



By feeding animals with dead cultures of bacteria or 

 with their separated toxines, a certain degree of immunity 

 may in certain cases be gradually developed. But this 

 method is so much less certain in results, and so much more 

 tedious than the others, that it has obtained no practical 

 applications. 



Active immunity of high degree developed by the methods 

 described may be regarded as specific, that is, is exerted only 

 towards the organism or toxine by means of which it has 

 been produced. A certain degree of immunity, or rather of 

 increased general resistance of parts of the body (for example 

 the peritoneum), can, however, be produced by the injection 

 of various substances bouillon, blood serum, solution of 

 nuclein, etc. (Issaeff). Also increased resistance to one 

 organism can be thus produced by injections of another 

 organism. Immunity of this kind, however, never reaches 

 a high degree. 



