INTRODUCTION 17 



ment of haemolysin be absorbed or fixed in the interac- 

 tion between antigen and antibody. This discovery 

 proved to be of the greatest importance and practical 

 value and underlies many modern serological clinical 

 tests. 



Wassermann, in 1906, the year following the dis- 

 covery of the Trepone7na pallidum, put the comple- 

 ment-fixation or deviation reaction of Bordet and 

 Gengou to a practical and successful test for the diag- 

 nosis of syphilis, and the so-called " Wassermann re- 

 action " was the result. Subsequently the principles 

 employed in Wassermann' s technic have been applied 

 to many other infectious diseases, notably gonorrhoea. 



In 1909, Ascoli, employing Traube's stalagmome- 

 ter, annomiced the " meiostagmin reaction," and de- 

 monstrated the feasibility of differentiating between 

 fluids containing mixtui'es of antigens and antibodies 

 by measui*ement of the drops contained in given vol- 

 umes. The method has been utilized in the diagnosis 

 of typhoid fever, tuberculosis, malignant tumors, foot- 

 and-mouth disease, and for the detection of many 

 lipoidal substances. 



Finally, reference should be made to certain para- 

 doxical reactions that have been observed in immu- 

 nology during recent years. Instead of the immunity 

 which commonly follows the injection of a foreign 

 protein substance into an animal, occasionally, al- 



