Complement Fixation 171 



bloods, and so led to the discovery that for each kind of 

 animal and for each individual animal the complement is 

 subject to very little variation. In the course of some three 

 years they were followed by the investigations of Neisser 

 and Sachs upon antigens, and made to subserve the useful 

 purpose of recognizing and differentiating antigenic sub- 

 stances. Thus, when a certain antibody and its comple- 

 ment are combined they can only attach themselves to the 

 particular specific antigen by which the antibody has been 

 developed. But, what is still more important, they have led 

 to the invention of methods by which the presence of specific 

 amboceptors may be determined where they are suspected, 

 and so have made possible means of arriving at a correct 

 diagnosis in certain obscure cases of disease in man. 



The most important of these measures is the Wassermann 

 reaction for the diagnosis of syphilis (q. v.). By careful 

 perusal of the chapter upon the method of performing the 

 Wassermann reaction the student will learn the general de- 

 tails of the technic, and can modify them to correspond to 

 the requirements of other cases in which complement fixa- 

 tion is to be studied. 



