434 IMMUNITY. 



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. 



In all the above instances the resulting immunity is 

 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). 

 A certain degree of immunity against one organism can 

 also be thus produced by injections of another organism. 

 Immunity of this kind, however, never reaches a high 

 degree, and has not a specific character. 



B. Passive Immunity. 



Action of the Serum of Highly-Immunised Animals. 



i. The serum of an animal A, in which there has been 

 developed a high degree of resistance by repeated and 

 gradually increased doses of the toxine of a particular 

 microbe, protects an animal B against a certain amount of 

 the same toxine when injected along with the latter, or a 

 short time before it. As would be expected, it has less 

 effect when injected some time afterwards, but even 

 then within certain limits, it has a degree of protec- 

 tive or palliative power. As by this method the serum of 

 animal A appears to neutralise the toxine, the term anti- ; 

 toxic has been applied to it. It also protects under like 

 conditions from infection with the corresponding microbe. 

 Thus an anti-diphtheritic serum prepared by injections of 



