ANTIBACTERIAL SERUM. 479 



In the original neutral mixture of crude toxin and antitoxin, both toxin and 

 toxoid were present. Any fresh crude toxin added contains both toxin and 

 toxoid. Some of the fresh toxin turns out some of the toxoid, and thus being 

 put out of action there is not enough poisonous material to cause death if 

 only one M.L.D. has been added to the neutral mixture. What remains 

 when the rearrangement of molecules has taken place is not toxin plus 

 toxoid, but toxoid plus toxoid. 



Antibacterial Serum. — The stages in the preparation of anti- 

 bacterial sera correspond to those in the case of antitoxic sera, 

 but living, or, in the early stages, dead cultures, are used instead 

 of toxin separated by filtration, and in order to obtain a setum of 

 high antibacterial 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 par- 

 ticular disease, and its virulence may be further increased by 

 the method oi 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 accompanied by the appearance 

 in the blood of protective substances, which can be transferred to 

 another animal. The law enunciated by Behring regarding 

 immunity against toxins thus holds good in the case of the liv- 

 ing 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 injected along 

 with them. Here again is presented the remarkable potency of 

 the antagonising substances in the serum, which in this case 

 lead to the destruction of the corresponding microbe. 



The antistreptococcic serum of Marmorek may be briefly 



