372 STUDIES IN IMMUNITY. 



puscles on the addition of guinea-pig alexin (0.3 of a cubic centi- 

 meter). No hemolysis, however, occurs if, instead of ordinary 

 heated bovine serum, the same serum previously treated with guinea- 

 pig corpuscles and separated from them by centrifugalization is 

 used. Such corpuscles have absorbed the sensitizer. 



Second: Ehrlich and Sachs think that the bovine serum (56 

 degrees) is the only sensitizing serum in their experiment. No 

 proof of this is given, and, as a matter of fact, the horse serum 

 also contains a sensitizer for guinea-pig corpuscles which is usually 

 stronger than the one in bovine serum. A mixture of horse serum 

 (0.3 of a cubic centimeter) and guinea-pig corpuscles (1 c.c. of a 

 5 per cent suspension) gives hemolysis on the addition of guinea- 

 pig alexin (0.3 of a cubic centimeter). It is not surprising that 

 fresh horse serum alone fails to hemolyze the blood, although it con- 

 tains both alexin and sensitizer, when we take into consideration, 

 as just shown, that the horse alexin fails to hemolyze these cor- 

 puscles even when they are well sensitized. It is to be noted in 

 passing that the horse sensitizer is very thermolabile, being almost 

 entirely deprived of its power by heating to 56 degrees. 



Third : Ehrlich and Sachs think that ox serum acts only as a 

 sensitizer in their experiment. 



Is it true that the bovine serum owes its entire or even the 

 greater part of its efficacy to its sensitizing property? May there 

 not also be, in addition to the sensitizer, some particular substance 

 in bovine serum that has not as yet been described in this or in 

 other sera? No such possibility has occurred to Ehrlich and Sachs, 

 who regard the bovine serum simply as containing a sensitizer. It 

 is evident that to decide such a question the sensitizing property of 

 the serum must first be removed. In other words, we must have 

 conditions in which the sensitizer not only need not but actually 

 does not enter into consideration. If, under such conditions, 

 heated bovine serum, although without a sensitizer, hemolyzes cor- 

 puscles with horse alexin, we must conclude that the serum con- 

 tains some other as yet unsuspected substance that is of capital 

 importance in the experiment. 



These conditions are easy to fulfill by adding well-sensitized 

 bovine blood corpuscles* instead of guinea-pig corpuscles to a 



* Previously treated with immune serum from the rabbit and then washed. 



