540 FRANK R. LILLIE 



chemical side-chains (receptors) capable of uniting with the agglu- 

 tinating substance. When such a union takes place the heads 

 of the spermatozoa must be supposed to become adhesive; if 

 they move about rapidly, there are more colhsions and hence 

 more agglutination. With stale spermatozoa, either the move- 

 ments are too slow to produce much agglutination, or the recep- 

 tors are cast off and lie free in the medium, so that their binding 

 does not affect the physical properties of the spermatozoa them- 

 selves. The latter possibility should be investigated, but was 

 not this summer owing to the multitude of other problems. 



A Httle light may be thrown on this problem by the results of 

 June 26: In that case 4 drops of a strong, but not definitely 

 standardized, solution of the agglutinating substance was added 

 to 4 cc. of a 3 per cent sperm suspension 3 hours old. The tube 

 was then centrifuged strongly and most of the spermatozoa 

 precipitated in a mass at the bottom; however the supernatant 

 fluid remained opalescent. Tested inmaediately with a fresh 

 sperm suspension the fluid gave a 17 to 25-second agglutinating 

 reaction. The tube was allowed to stand five minutes longer and 

 was then tested again; the precipitated sperm remained in a 

 solid mass, but the supernatant fluid had become negative; it 

 contained no more free agglutinating substance. The quantity 

 of sperm in suspension seemed much too small to account for the 

 neutralization, which I am inclined to attribute to free receptors. 

 But no really adequate test was made. 



As to the interpretation to be given to the reversal of aggluti- 

 nation of the sperm it may be supposed either, (1) that the ad- 

 hesive condition on which the agglutination depends exists only 

 during an early union of the agglutinating substance with the 

 sperm receptors and is lost as the union becomes firmer; or (2) 

 that the bound receptors are cast off by the sperm. In view of 

 the nature of the mechanism of the fertilization process, discussed 

 beyond, I am inclined to lean to the second hypothesis. 



