2/4 PHYSIOLOGICAL CHEMISTRY. 



has received much elucidation through numerous observations 

 of recent years. One of the most important of these is con- 

 cerned with the so-called Pfeiffer experiment. 



Pfeiffer's Phenomenon. In his famous experiments on 

 the behavior of cholera bacteria Pfeiffer found that the serum 

 of an animal which had been immunized against cholera, when 

 tested in vitro against the vibrios, seemed deficient in bacteri- 

 olytic power, possessing no greater activity, evidently, than 

 that due to the proteolytic ferment of the normal serum. Ac- 

 tivity may be given to the immunized serum, however, by in- 

 jecting it back into the peritoneal cavity of the animal ; cholera 

 vibrios injected at the same time are quickly destroyed. The 

 action is strictly specific, since typhoid bacilli injected in the 

 same way remain active. It was found also that the same 

 result can be reached with the vibrios by adding, in vitro, fresh 

 normal serum to the latent immunized serum. The vibrios 

 succumb as they did in cor pore, showing that a vital action is 

 not in play. Numerous similar observations were made by 

 Bordet and others. From all these experiments it is evident 

 that at least two things are concerned in the bacteriolytic action 

 and the analogous hemolytic phenomena. The immune body 

 developed in the course of immunization does its work as a 

 cell destroyer, whether a blood corpuscle or a bacterium, only 

 by the aid of something normally present in fresh serum. The 

 specific immune body was found to be thermostable, that is it 

 withstands a temperature of 55-7o without loss of its spe- 

 cial properties. If after being warmed to this extent the im- 

 mune serum is cooled to below 55 and mixed with fresh nor- 

 mal serum the full cytolytic activity appears. On the other 

 hand the ferment in the normal serum is thermolabile ; a tem- 

 perature of 55 or above destroys it permanently. For this 

 thermolabile normal ferment Ehrlich proposed the name addi- 

 ment. This is the same as the alexin body. The term com- 

 plement is also used to describe the same thing which seems 

 necessary to make the specific immune body really active. 



The Side Chain Theory. Thus far we have been con- 



