154 ANTIGENS AND THE TECHNIC OF SERUM REACTIONS 



extensively utilized to demonstrate the presence of various specific 

 immune antibodies. If a specific immune body (as for example, 

 the serum of an animal immunized to typhoid bacilli) is heated to 

 55 C. for half an hour, then added to a suspension of typhoid bacilli 

 together with normal unheated serum, a union between the bacilli, 

 the specific antibody of the serum (amboceptor, substance sensibili- 

 trice) and the complement (alexin) will take place. If the proportions 

 of the three reactive bodies are correct, all the complement or alexin 

 will be bound, provided the mixture is incubated a few hours at 37 

 C. If, now, red blood cells and inactivated immune serum specific 

 for the red blood cells are added to the mixture of bacteria, immune 

 body and complement, no hemolysis should be noticed, because the 

 complement is quantitatively anchored to the bacteria-immune serum 

 complex. If, on the other hand, the inactivated immune serum added 

 to the suspension of typhoid bacilli be not typhoid immune serum, 

 complement will not be bound to the bacteria, for the specific ambo- 

 ceptor or substance sensibilitrice will not be present. The complement 

 or alexin, therefore, is not anchored to the bacteria, and it is free to 

 act when the red blood cells and their specific inactivated serum are 

 added to the mixture of bacteria and serum. Under this condition 

 hemolysis occurs, because the red blood cells, inactive immune body 

 and complement unite. The production of hemolysis being visible, 

 it acts as an indicator in such instances. Wassermann and his asso- 

 ciates have utilized this method of "fixation of complement" for the 

 serologic diagnosis of syphilis, and gradually a relatively large number 

 of diagnoses of clinical importance have been developed along the 

 same lines. 



The Determination of Specific Antibodies by the Method of Complement 

 Fixation. Principle Involved. When an antigen (bacteria, erythro- 

 cytes, tissue cells, protein, or other substance which stimulates specific 

 antibody formation) is mixed intimately with its specific inactivated 

 immune serum and fresh normal complement a firm union of the 

 three components takes place. 1 The result of this union is an injury 

 or destruction of the antigen. If the antigen be bacterial cells or 

 tissue cells there is usually no visible change in the gross appearance 

 of the mixture, and cultural or chemical investigation must be relied 

 upon to demonstrate the lytic process. Erythrocytes, on the other 

 hand, undergo changes in the presence of inactivated specific immune 

 serum and complement which result in the liberation of hemoglobin, 



1 Bordet and Gengou, Ann. Inst. Past., 1901, xv, 290. 



