PROPERTIES OF ANTISENSITIZERS. 293 



This experiment is not indispensable, as a similar conclusion 

 might be drawn with assurance from an observation that has been 

 made concerning normal rabbit serum. We have already noted 

 that on adding a little normal rabbit serum, 56 degrees, to a mix- 

 ture of sensitized corpuscles, antiserum and alexin, in which no 

 hemolysis is present, hemolysis appears; we must conclude, then, 

 that the normal serum contains a substance that can replace the 

 specific sensitizer in its union with the antitoxin, at least in part. 

 That this substance is not to be regarded as a rabbit > ox sensi- 

 tizer preexistent in small amounts in normal rabbit serum is evident 

 from the fact that the normal serum does not sensitize ox cor- 

 puscles to alexin. But in order to be quite certain of this point 

 and to forestall any possible objection, we may ascertain whether 

 normal rabbit serum that has been treated with an excess of ox 

 corpuscles acts in a similar manner. 



Let us place 1 c.c. of defibrinated ox blood in a large tube, fill with 

 salt solution, centrifugalize, and then remove the supernatant fluid, 

 leaving a sediment of blood corpuscles to which 1 c.c. of heated 

 rabbit serum is added. On the following day we centrifugalize, 

 remove the supernatant serum and add to it the fresh sediment 

 of another cubic centimeter of washed ox blood. We may hope 

 that two successive contacts with ox corpuscles will have absorbed 

 all the combinable substances in the normal serum. We then 

 prepare sensitized and washed ox blood as in the former experi- 

 ment. 



Two tubes, A and B, are prepared, containing, each, 0.1 of a cubic 

 centimeter of sensitized washed blood, 0.3 of a cubic centimeter of 

 antiserum and 0.1 of a cubic centimeter of guinea-pig alexin; to 

 tube A is then added 0.2 of a cubic centimeter of the normal rabbit 

 serum treated with ox blood as described. The corpuscles are 

 hemolyzed in 10 minutes in tube A, but remain intact in tube B. 

 A control shows that the treated normal serum in the same doses 

 does not hemolyze a mixture of antiserum, alexin and non-sensi- 

 tized corpuscles. 



The same results are obtained by using in place of normal rabbit 

 serum, rabbit > ox serum that has previously been deprived of 

 its specific activity by two successive contacts with ox corpuscles. 

 Such treated rabbit > ox serum still combines with the anti- 



