I 



CYTOLYSINS, BACTERIOLYSINS, AND HEMOLYSINS 163 



certain diseases, and in the recognition of certain organic sub- 

 stances. This second use is called variously absorption or fixation 

 of complement, or, after the name of its discoverers, the Bordet- 

 Gengou phenomenon. 



Fixation of Complement and Its Utilization. The method of 

 complement fixation is one that enables us to determine the pres- 

 ence or absence of cytotoxic, cytolytic, or similar antibodies in a 

 serum. Inasmuch as such substances are generally present in the 

 serum of a diseased individual, the determination of their presence 

 may constitute in such cases a diagnosis of the disease. A specific 

 example, the demonstration of fixation of complement by use of 

 antityphoid serum, will first be discussed. Five different solutions 

 are always needed in carrying out a test of this kind. 



1. Suspension of Bacillus typhosus (antigen). 



2. Heated serum of rabbit immunized against 1 (amboceptor). 



3. Normal serum, usually taken from guinea-pig (complement). 



4. Red blood-cells. Those of sheep generally used (antigen). 



5. Heated serum of rabbit immunized against 4 (amboceptor). 

 Suppose that 1 and 2 are mixed, and a small amount of 3 added. 



Evidently the complete bacteriolytic system is present and bac- 

 teriolysis should occur. This is difficult to demonstrate micro- 

 scopically, however, and would not be demonstrated at all in that 

 manner if an excess of the first antigen or suspension of bacilli is 

 used. It is evident that the complement added will be used up or 

 " bound " by the combination of bacillus and amboceptor. No. 4 

 and o are next added. They unite with each other, but, as all 

 the complement has been used up, there can be no hemolysis. 

 The fact that hemolysis does not occur is proof, therefore, that the 

 complement has been removed. Suppose that, instead of the blood 

 of a rabbit that has been intentionally immunized to the disease, 

 the serum from a patient suspected of having the disease is used. 

 If hemolysis does not occur, then amboceptors for B. typhosus 

 are present in the patient's blood, and the diagnosis of the disease 

 would be positive. If hemolysis does occur, evidently the patient's 

 serum lacks amboceptor specific for typhoid, and the diagnosis 

 would be negative. The test may be reversed also, and some 

 organism suspected of being Bacillus typhosus may be substituted 

 for No. 1, and the same technic carried through. A lack of hemo- 



