riih] PRECIPITIN 



By D. A. Welsh, m.a., b.sc, m.d.. m.r.c.p. Win., and H. G. 



(From the Laboratories of Physiology and of Pathology in 

 the University of Sydney.) 



Introductory. 



Phenomena of precipitation : 



(a) Relation of antiserum to precipitate. 



(b) Total and partial interactions. 



(e) Relation of antigen to precipitate. 

 Phenomena of inhibition. 

 Co lu o 

 References. 



Introductory.— The different phenomena of immunisation 



are but different aspects of the response of the animal 

 body to the introduction of alien substances within its 

 tissues, and the precipitin reaction is one form of this 

 response. When the blood serum of an animal that has 

 received repeated injections of some alien protein is mixed 

 outside the body with a solution of this alien protein, then 

 precipitation may occur. This, apparently one of the 

 simplest of the immunity reactions, is yet one of the hardest 

 to interpret. We do not propose to discuss what corres- 

 ponding property has been acquired by the blood in viro, 

 nor what is its relation to tin? general defensive mechanism 

 (1). It is with the interaction of antiserum and antigen, 

 indicated by a precipitate in vitro, that we are now con- 

 cerned. 



From the beginning we have looked upon the reaction as 

 taking place between known weights of the interacting 

 substances. In our later work the weighing of the pre- 



