SEROLOGY AND SYSTEMATICS 69 



serology concerns essentially antigen-antibody responses. That is, 

 certain foreign substances (called antigens and formerly regarded 

 as proteins though now it is recognized that other substances than 

 protein may be antigenic), when injected into a host, may elicit 

 the formation, in the host, of other substances (called antibodies, 

 likewise generally regarded as proteinaceous) which may agglutinate 

 or otherwise affect the foreign substance. Various species of domes- 

 tic animals may serve as the host although rabbits are most fre- 

 quently used. 



Chester has listed the types of reactions which were utilized 

 up to 1937. Since his review, the first method to be discussed 

 below, the precipitin reaction, has become the most widely used. 

 The precipitin reaction is probably the simplest of the various 

 methods of evaluating antigen-antibody reactions. In this method, 

 one mixes aliquots of the antigen in varying dilutions with the anti- 

 body preparation (antiserum); this mixture produces an amount of 

 precipitate corresponding to the "strength" of the reaction, and 

 the precipitate is appropriately measured. In addition to the precipitin 

 reaction various reactions classified as anaphylaxis reactions have 

 been utilized. In principle these last methods involve sensitizing a 

 host, then later injecting into the host a second dose of antigen 

 preparation. The second injection may induce some physiological 

 response such as inflammation or spasms. An interesting modification 

 of the anaphylaxis reaction is known as the Schultz-Dale technique. 

 A sensitized virgin female guinea pig is killed, and the uterus removed, 

 placed in Ringer's solution, and attached to a kymograph. The antigen 

 preparation is added directly to the uterus, and the degree of uterine 

 contraction is measured on the kymograph. A third type of reaction 

 involves the destruction (or agglutination) of particulate antigen 

 carriers such as bacteria, blood cells, pollen or other unicellular bodies 

 by antisera from sensitized hosts. Complement fixation, a fourth type 

 of reaction, utilizes the knowledge that a non-specific, heat labile 

 substance (complement) which participates, essentially, in the antigen- 

 antibody interaction, is used up in the process. Therefore, in principle 

 one measures the presence or absence of residual complement, follow- 

 ing the exposure of the antiserum to an unknown antigen preparation. 

 Residual complement is measured by comparing the efficiency of a 

 second reaction to a standard antigen preparation, for example sheep 

 blood cells. Complement fixation would be suitable as an indirect 

 indicator of an interaction which could not be followed visually. 

 In another type of reaction, the Aberhalden reaction, the serum and 

 the antiserum used to test it are mixed in a dialysis membrane. 

 Subsequently one tests the external medium with ninhydrin for 



