236 DEVIATION OF COMPLEMENT TEST 



powerful antiserum a reaction can usually be obtained in dilutions 

 so high that proof of the presence of proteids is barely obtainable 

 by ordinary chemical means. The weak point in the method is 

 that it is never possible to say exactly how much of the proteid 

 matter of the clot has been dissolved, and thus to compare the 

 effect of the antiserum on the solution with its action on diluted 

 serum of man and of other animals. Given a sample of unaltered 

 and undried serum, the test can be carried out with almost 

 complete certainty ; but this is rarely, if ever, possible in actual 

 practice. 



Another test, based on Gengou's reaction, has recently been intro- 

 duced by Neisser and Sachs. It is carried out in the following 

 way : A hsemolysin for ox corpuscles is prepared by injecting 

 these bodies into a rabbit. Another rabbit is injected with human 

 blood, so as to lead to the production of a precipitin. When the 

 test is to be made the fresh serum of the latter animal (or if only 

 stale serum is at hand, some fresh normal rabbit's serum must be 

 added to supply complement) is added to the fluid to be tested. 

 If human serum is present, even in an amount so small that no 

 precipitate is formed, the antigen and antibody combine and with- 

 draw the complement from solution. To test this ox corpuscles 

 are sensitized with the heated (decomplemented) serum of the first 

 rabbit and thoroughly washed, and some of the mixture added. 

 If the complement has been withdrawn, of course no haemolysis 

 will occur. Certain obvious controls are employed to demonstrate 

 that the corpuscles were actually sensitized, and that complement 

 was present in the rabbit's serum before the addition of the fluid 

 suspected of containing human blood. 



This test is extraordinarily sensitive, Neisser and Sachs finding 

 that the millionth part of a cubic centimetre of human serum was 

 readily demonstrable. They claim also that it is more specific 

 than the ordinary precipitin test, it being necessary, for instance, 

 to use T^Viy c.c. of ape's serum to get the same result. But the 

 technique is complicated, and it appears, moreover, that comple- 

 ment may be abstracted in an altogether non-specific manner by 

 substances other than the combination of antigen and antibody. 

 Thus Uhlenhuth examined some spots of blood on a sack which a 

 cabdriver (who was found dead) used as a seat, and found it 

 brought about a fixation of complement, though it gave no reaction 

 with the precipitin test. He then tested the material of which 

 the bag was made, and found it also had the power of absorbing 



