140 IMMUNE SERA 



Von Pirquet and Schick's Theory. It was diffi- 

 cult to account for the long incubation period in 

 " serum sickness." With poisons capable of self- 

 multiplication (bacteria, etc. ) this period was usually 

 referred to the time necessary for them to accumu- 

 late in sufficient number and virulence to produce 

 symptoms. But serum is not a poison capable of 

 multiplication. Pfeiffer's work on the endotoxins 

 led to the view that the antibodies played an impor- 

 tant part in bringing on the symptoms by setting 

 free the endotoxins. The results of these observa- 

 tions are very closely related to von Pirquet and 

 Schick's explanation of the production of serum 

 disease. The endotoxic theory, in the sense of bac- 

 teriolysis, naturally cannot be applied to albumi- 

 nous substances in solution. We can only accept 

 it in the sense that by means of the reaction between 

 the antibodies and the antigen the poisonous sub- 

 stance is formed. 



It is of course at once apparent that the formation 

 of antibodies requires a definite period of time. The 

 general idea underlying von Pirquet and Schick's 

 theory of serum sickness is that the injection of the 

 horse serum into man causes the development of 

 specific reaction products which are able to act 

 upon the antigens introduced. These antibodies 

 encounter the antigens, i.e., some of the serum still 

 present in the body, and so give rise to a poisonous 

 substance. This accounts also for the cases of 



