INFECTION AND IMMUNITY. 459 



Toxic ptomaines are probably not conspicuously con- 

 cerned in producing the characteristic symptoms of 

 infection, as they are absent from cultures of certain 

 highly pathogenic bacteria. 



In some instances the production of the poisonous 

 principles, even under artificial conditions of cultiva- 

 tion, is of a most astonishing nature, and poisons result 

 that, in the degree of their toxicity, exceed anything 

 hitherto known to us. For instance, the potencies of 

 the poisons that have been isolated from cultures of 

 bacillus diphtherice and of the bacillus of tetanus have 

 been carefully determined by experiments upon ani- 

 mals, and it has been found that 0.4 milligramme of 

 the former is capable of killing eight guinea-pigs, each 

 weighing 400 grammes, or two rabbits, each weighing 3 

 kilogrammes (Roux and Yersin 1 ); and that 0.0001 mil- 

 ligramme of the latter will produce tetanus in a mouse, 

 with all the characteristic manifestations of the disease 

 (Brieger and Cohn 2 ). 3 



In short, infection may be best conceived as a contest 

 between the invading organisms on the one side and the 

 resisting tissues of the animal body on the other, the 

 weapons of offence of the former being the poisonous 

 products of their growth, the toxins, and the means of 

 defence possessed by the latter being substances which 

 are, so to speak, antidotal to these poisons. To these 

 substances possessed by the animal body for resisting 

 infection the name "alexines" has been given by 

 Buchrier, while the name ct defensive proteids" is sug- 



1 Annales de 1'Institut Pasteur, tome iii., 1889, p. 287. 



- Zeitschr. fur Hygiene u. Infektionskrankheiten, 1893, Bd. xv. Heft i. 



3 Through the use of more recently devised methods we are enabled to in- 

 crease still further the toxicity of these poisons ; especially is this the case 

 with regard to the diphtheria toxin. 



