ANTITOXINS 83 



the tetanus toxin. But the usual source from which 

 antitoxins are obtained for practical purposes is the 

 blood of animals which have been rendered immune. 

 The diphtheria antitoxin, which is now extensively 

 and successfully employed for the cure of diphtheria, 

 is obtained from the blood of horses which have been 

 immunised by repeated inoculations with the toxic 

 products of the diphtheria bacillus. 



A most interesting question presents itself in con- 

 nection with the discovery of the antitoxins : Is the 

 animal which has been immunised against any par- 

 ticular toxin also immune for other poisonous sub- 

 stances of the same class ? This question has been 

 definitely answered in the negative by experimental 

 investigation. In other words, each specific toxin 

 causes the development in the body of the immune 

 animal of a specific antitoxin which has no neutralis- 

 ing action upon any other toxin than that which gave 

 rise to its production. An animal which has been 

 immunised against the toxic action of ricin is poi- 

 soned by the usual fatal dose of abrin. The tetanus 

 antitoxin affords no protection against the poisonous 

 products of the diphtheria bacillus and vice versa. 



The antitoxins protect susceptible animals from in- 

 fection when introduced by inoculation at the same 

 time or in advance of the disease germs against 

 which they have a specific action. They may also, in 



