ANTIMICROBIC SERUM. 479 



though in much less concentration than in the blood. It 

 is present in the milk, and a certain degree of immunity can 

 be conferred on animals by feeding them with such milk, 

 as has been shown by Ehrlich, Klemperer, and others. 

 Klemperer also found traces of antitoxine in the yolk of 

 eggs of hens whose serum contained antitoxine. 



Antimicrobic Serum. The stages in preparation of 

 antimicrobic sera correspond to those in the case of 

 antitoxic sera, but living, or, in the early stages, dead 

 cultures are used instead of the toxine separated by 

 nitration, and in order to obtain a serum of high antimicrobic 

 power, a very virulent culture in large doses must be 

 ultimately tolerated by the animal. For this purpose a 

 fairly virulent culture is obtained fresh from a case of the 

 particular disease, and its virulence may be further increased 

 by the method of passage. This method of obtaining a 

 high degree of immunity against the microbe is specially 

 applicable in the case of those organisms which invade the 

 tissues and multiply to a great extent within the body, and 

 of which the toxic effects, though always existent, are 

 proportionately small in relation to the number of organisms 

 present. The method has been applied in the case of the 

 typhoid and cholera organisms, the bacillus of bubonic 

 plague, the bacillus coli communis, the pneumococcus, 

 streptococcus (Marmorek), and many others. In fact, it 

 seems capable of very general application. 



The important result obtained by such experiments is, 

 that if an animal be highly immunised by the method 

 mentioned, the development of the immunity is accom- 

 panied by the appearance in the blood of protective sub- 

 stances, which can be transferred to another animal. The 

 law enunciated by Behring regarding immunity against 

 toxines thus holds good in the case of the living organisms, 

 as was first shown by Pfeiffer. The latter found, for 

 example, that in the case of the cholera organism, so high 

 a degree of immunity could be produced in the guinea-pig, 

 that .002 c.c. of its serum would protect another guinea- 

 pig against ten times the lethal dose of the organisms, when 



