THEORIES OF IMMUNITY. 



linked to the sheep's corpuscles, and hemolysis 

 of the latter ought to have occurred. The im- 

 mune body therefore was not here. The sheep's 

 corpuscles of the original mixture were, of 

 course, in the deposit separated by the centrif- 

 ugalization. This was now taken, stirred up 

 with four cubic centimeters of .75 per cent salt 

 solution and there was added .8 c. c. of fresh 

 goat's serum (containing of course complement). 

 The mixture was placed at 37° C. for two 

 hours, and at the end of this time there was 

 found to have occurred hemolysis of the cor- 

 puscles. During the fifteen minutes that the 

 original mixture was kept at 40°, therefore, the 

 immune body in the immune goat's serum had 

 united itself to the sheep's red corpuscles, as was 

 evidenced by the fact that when the latter were 

 exposed to fresh complement, hemolysis occurred. 

 As remarked above, complement cannot cause 

 hemolysis by itself. The method of the experi- 

 ment is that three factors are necessary to the 

 occurrence of a given hemolysis: the red-blood 

 cells to be acted on; a body resistant to heat, 

 occurring in the serum of the immune animal 

 (immune body) ; and a body susceptible to 



