IMMUNITY. 385 



substances. The blood of healthy men in 

 many cases neutralizes the diphtheria toxin 

 (Abel), the typhoid toxin' (Stern), and the toxin 

 of cholera (Metschnikoff), while it has no effect 

 upon tetanus toxin, snake venom and abrin. 

 (From the first observation, Wassermann has 

 drawn the far too hasty conclusion that in such 

 cases the healthy individuals had previously 

 resisted a mild attack of diphtheria.) I have 

 called attention previously (p. 183) to a similar 

 observation of Hericourt and Richet to the 

 effect that the serum of healthy dogs protects 

 rabbits against staphylococcus pyaemia. 



2. Antitoxins that are formed specifically in 

 serum act in vitro upon poisons of a specific- 

 ally different character in the same manner as 

 upon poisons specifically similar, while the con- 

 verse does not always obtain : " anti-venin " 

 annuls the poisonous effect of abrin, but not of 

 diphtheria toxin, tetanus toxin or ricin ; aiiti- 

 abrin neutralizes the toxic effect of snake 

 venom, diphtheria toxin and ricin, but not that 

 of tetanus toxin ; tetanus antitoxin is antago- 

 nistic to snake venom, but powerless against 

 ricin and abrin ; rabies serum is potent against 

 snake venom, but impotent against the diph- 

 theria and tetanus toxins, and against ricin and 

 abrin; streptococcus serum is potent against 

 snake venom, powerless against the others ; 

 25 



