THE TECHNIQUE OF SERUM REACTIONS 261 



In all hemoljrtic tests the time element is important. No hemo- 

 lysis should be adjudged as incomplete unless at least one hour has 

 elapsed. 



It is often necessary to carry out hemolytic tests on the blood 

 corpuscles of one human being with the serum of another in order to 

 determine the advisability of performing transfusion. In this case, the 

 serum of the recipient is mixed with a corpuscle emulsion of the cells of 

 the donor, and vice versa. Since it is often difficult to obtain much 

 blood for these tests, the writers have found it convenient to make the 

 test in throttle pipettes, instead of in test tubes. Bj' this technique, ten 

 or fifteen drops of blood and a very small amount of serum will suffice. 

 It should be stated, however, that whenever sufficient quantities of 

 serum can be obtained this technique should not be employed. 



The Determination of Antibodies in Sera by Complement Fixation. — 

 The principle of complement fixation, discovered by Bordet and Gengou' 

 in 1901, has been utilized both in bacteriological investigations, and in 

 practical diagnosis for the determination in serum of the presence of 

 specific antibodies. Although spoken of in another section of this book, 

 it may be well to review, briefly, the principles of the Bordet-Gengou 

 phenomenon. The reaction depends upon the fact that when an antigen, 

 i.e., a substance capable of stimulating the formation of antibodies in 

 animals or man, is mixed with its inactivated antiserum, in the presence 

 of complement, the complement is firmly fixed by the combined immune 

 body and antigen in such a way that it can no longer be found free in 

 the mixture. If such a mixture is allowed to stand at a suitable tem- 

 perature for an hour or more, and to it is then added an emulsion of red 

 blood cells together with a suitable quantity of inactivated hemolytic 

 serum, no hemolysis will take place, since there is no free complement 

 available to complete the hemolytic system. If, on the other hand, the 

 original mixture contains no antibody for the antigen used, the comple- 

 ment present is not fixed and is available for the activation of the 

 hemolytic serum later added. 



The reaction thus depends, in principle, intimately upon the fact 

 that neither antigen ' alone, nor amboceptor (antibody) alone, can fix 

 complement, but that this fixation is carried out only by the combina- 

 tion of antigen plus amboceptor. Any specific amboceptor can be deter- 

 mined by this method, provided the homologous or stimulating antigen 



J Bordet and Gengou, Ann. de I'inst. Pasteur, xv, 1901. 

 ' Bordet and Oay, Ann. de I'inst. Pasteur, xx, 1906. 



