150 A MANUAL OF BACTERIOLOGY 



an animal injected with sub-lethal doses of a bacterial 

 toxin, e.g. diphtheria toxin, acquires a tolerance towards 

 the toxin, becomes immunised, and a substance is de- 

 veloped in the blood that antagonises the toxin which 

 was injected ; this substance is known as antitoxin. If 

 bacteria be injected, the fresh blood in vitro has a solvent 

 action on the bacteria (bacteriolysis) ; if blood- corpuscles 

 be injected, the fresh blood has a solvent action on the 

 same kind of blood-corpuscles (haemolysis) ; if cells be 

 injected, the blood has a solvent action on the cells 

 (cytolysis), and so on. If ferments be injected, anti- 

 ferments are formed and will prevent the specific action 

 of the ferment. With doubtful exceptions, 1 it is only 

 complex bodies of protein nature, or allied to the proteins, 

 which give rise to the production of anti-bodies on inocula- 

 tion ; alkaloids, carbohydrates, mineral poisons, etc., do 

 not give rise to anti-bodies, though some insusceptibility 

 to them may be produced (see also p. 206). Any substance 

 which gives rise to an anti-body may be termed an anti- 

 gen. These anti-bodies, etc., may first be considered, 

 after which immunity will be discussed. 



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 



1 Ford has described the formation of an anti-body by the injection 

 of a poisonous glucoside derived from fungi. 



