356 BACTERIOLOGY. 



protective inoculation, is of very short duration ; 

 in diphtheria it varies from 8-14 days to 10 

 weeks at most. It is not possible to immunize 

 effectively against diphtheria with curative 

 serum, a fact which on account of the con- 

 fidence we are justified in attaching to really 

 specific protective inoculations is a matter of 

 practical importance. This result of experi- 

 ment is in full accord with clinical experience 

 which has shown that an attack of diphtheria 

 confers little or no immunity. Although it 

 is generally possible to bring about some small 

 degree of immunity with diphtheria serum 

 the immunization does not necessarily have 

 anything to do with the presence of special 

 anti-substances. The slight protective effect 

 that has been observed might arise from the 

 fact that when old cultures are used we intro- 

 duce into the animal besides the poisons other 

 bacterial cell-substances which are capable of 

 producing immunity ; or it may be that the 

 effect is caused simply by another sort of action 

 due to the suitable stimulative action of a 

 sufficiently active chemical body. 



In line with Behring's conception, R. Pfeif- 

 fer has prepared a curative serum against 

 typhoid fever by inoculation of animals with 

 typhoid bacteria. Marmorek, also, who ob- 

 tained very virulent cultures of streptococci by 



...} :* noli 



