INFECTION AND IMMUNITY. 545 



solubility in alkalies, resistance to the boiling tempera- 

 ture, attraction of leucocytes (positive chemotaxis ! ), and 

 pyogenic powers. 



There is as yet little agreement of opinion as to the 

 chemical nature of toxins ; but it is probable that the 

 group comprises different bodies of the nature of globu- 

 lins, nucleo-albumins, peptones, albumoses, and enzymes 

 or ferments. 



Toxic ptomams 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 particular instances the production of poisonous 

 principles, even under artificial conditions of cultivation, 

 is most astonishing, and poisons are generated 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 bacterium diphtheria? 

 and of bacillus tetani have been carefully determined 

 by experiments upon animals, 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 2 ); and that 0.0001 milligramme of the latter 

 will produce tetanus in a mouse, with all the character- 

 istic manifestations of the disease (Brieger and Cohn 3 ). 4 



iSee Chemotaxis. 



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



sZeitschrift fur Hygiene und Infektionskrankheiten, 1893, Bd. xv. 

 Heft 1. 



4 By the use of more recently devised methods we are enabled to 

 increase still further the toxicity of these poisons ; especially is this 

 the case with regard to the diphtheria toxin. 



35 



