IMMUNITY AND SUSCEPTIBILITY 709 



sary to have a rabbit immunized with some hemolytic antigen, such as 

 sheep or human erythrocytes. There is developed in the serum of the 

 rabbit the hemolysin for sheep or human corpuscles which when com- 

 bined with these corpuscles will cause a liberation of hemoglobin. 

 In the rabbit serum there are both hemolytic amboceptors and comple- 

 ment. It is necessary to heat this hemolytic rabbit serum to 56 for 

 thirty minutes in order to destroy its complement and also it is necessary 

 to find out accurately the amount of guinea-pig serum- which will com- 

 plement the resulting hemolytic amboceptor. This definite amount of 

 complement having been determined, it is mixed with syphilitic antigen 

 plus the syphilitic amboceptor, mentioned above, and allowed to incu- 

 bate for one hour and thirty minutes at 37. If the serum is from a 

 case of syphilis the antibodies (amboceptors) will be present and com- 

 bine with the antigen, and also the guinea-pig serum complement. The 

 next step in the technic is to add to the above-mentioned mixture the 

 hemolytic amboceptor and its antigen, sheep corpuscles. If the com- 

 plement has been bound there will be none left to combine with the 

 hemolytic amboceptor and no hemolysis of the sheep or human cor- 

 puscles will result. If the patient's serum does not contain syphilitic 

 amboceptors or antibodies, the complement will not be bound and 

 hemolysis will result. This test has been designated as the Wassermann 

 test on account of the man first working it out in the case of syphilis, 

 and has shown itself to be very efficient in the diagnosis of this disease 

 in suspected cases. Many modifications of this test have been devised, 

 some of which are very accurate. 



The fixation of the complement may be made use of in the detection 

 of any bacterial antibody, the procedure being approximately the same 

 as above indicated and the hemolytic system used as an indicator as in 

 the case of syphilis. The antigen, however, is different. When working 

 with specific bacteria a suspension of bacterial cells in 0.85 per cent 

 sodium chloride solution constitutes the antigen. 



Cytotoxins and Cytolysins. The names cytotoxin and cytolysin are 

 used synonymously and are applied to those substances in sera and 

 other body fluids which have the power of destroying cells other than 

 erythrocytes. In a broad sense any substance destroying a cell would 

 be cytotoxic but the terms are usually applied in the more limited 

 manner, as above indicated. 



Cytotoxins are produced in the same manner as other antibodies. 



