3iO BACTERIOLOGY. 



the protecting substances. That they are in- 

 tegral elements of the living protoplasm of the 

 bacterial cell appears certain ; they are supposed 

 to possess a higher phosphorus content than 

 the toxin, and they pass with greater diffi- 

 culty through porcelain filters. We must infer 

 from the protective action of impotent cultures, 

 that these substances are the expression of the 

 more immutable qualities of the species, and 

 not, like the poisons, of the variable character- 

 istics. It may be legitimately conjectured that 

 foreign protoplasm and active proteid are usu- 

 ally able to confer some sort of immunity al- 

 though in varying degrees according to nature 

 and origin. 



If experiments are made with proteid-like 

 poisons of diverse origin (with' the vegetable 

 poisons abrin and ricin, as Ehrlich has done, 

 and as Roux, Behring and Tizzoni have done 

 in a similar way with tetanus and diphtheria 

 poisons), it is seen that the animal organism 

 comports itself toward . these poisons just as 

 toward arsenic, alcohol, nicotine or morphine. 

 The . organism accustoms itself to increasing 

 quantities of the specific poison, and becomes 

 tolerant of it, but is not affected to the ex- 

 tent of acquiring immunity, and is not, prop- 

 erly speaking, immunized. If true immunity 

 be obtained with " metabolic products," bodies 



