ANTI-BODIES 179 



carbohydrates, mineral poisons, etc., do not give rise to 

 anti-bodies, though some insusceptibility to them may 

 be produced (see also p. 253). Any substance which gives 

 rise to the formation of an anti-body is termed an antigen, 

 and a blood-serum containing anti-bodies is termed an 

 immune serum. A remarkable property of anti-bodies is 

 their extreme specificity ; as a rule they react only with 

 the antigen which has produced them, i.e. antigen and 

 anti-body must be homologous for interaction to take place. 



Anti-bodies are probably formed for the most part in 

 the spleen, lymph-glands and bone-marrow by leucocytes, 

 or by endothelial cells, or by both. 



ANTITOXINS. The anti-bodies produced by the inocu- 

 lation of an animal with bacterial toxins or toxic proteins 

 (e.g. ricin, abrin, and snake-venom) are known as anti- 

 toxins, and are of considerable practical importance. An 

 animal injected with increasing amounts of the toxin 

 acquires a high degree of immunity, and its blood-serum 

 injected into a second animal confers on the latter a 

 similar immunity against the same toxin, but not against 

 other toxins ; the serum is specific. The anti-serum 

 formed by the injection of toxin is antitoxic and not 

 anti-microbic, and the diphtheria bacillus will grow and 

 multiply in diphtheria antitoxin. Since, however, the 

 pathogenic effects of an organism such as the diphtheria 

 or the tetanus bacillus are caused by the toxin which it 

 forms, the antitoxin will counteract the effects of the 

 micro-organism, as well as of its toxin. The neutralisa- 

 tion of the micro-organism, however, may not be quite 

 complete, a certain amount of local reaction or necrosis 

 ensuing. 



Antitoxins are prepared by injecting animals prefer- 

 ably horses, but goats, rabbits, etc., may also be employed 

 with bacterial toxins or with toxic proteins, such as 

 snake-venom. 



122 



