IMMUNITY. 305 



from this to be strictly " specific," or still more 

 precisely expressed, " isopathic." 



Still another step was taken in the same 

 direction. The experiments described above 

 were carried out with living microbes. Even 

 when attenuated cultures were used it some- 

 times happened that some of the inoculated ani- 

 mals died either through accidental inoculation 

 of too large amounts of material or through 

 greater individual predisposition to disease, 

 thus affording direct proof that attenuated 

 material might, by passing through suitable 

 animals, again become virulent. The attempt 

 was made therefore to dispense altogether with 

 the living parasites and their attenuated modi- 

 fications. 



Inoculation With Metabolic Products Protect- 

 ive Substances and Poisons Immunity Does 

 Not Depend Upon Habituation to Poison. 

 Panum in 1874 first established the fact that 

 the poisonous action of bacteria is due to solu- 

 ble poisons formed by the bacteria, but separ- 

 able from them, and that this poisonous action 

 could be advantageously combated indirectly, 

 namely, by combating the germs forming the 

 poison. It was afterwards discovered by Koch 

 in 1878, by Chauveau in 1880, and later by 

 many other observers that a number of patho- 

 genic germs actually injure the organism less 



20 



