122 PROBLEMS OF FERTILIZATION 



agglutinating substance is found to be absent from the 

 supernatant fluid. If a lesser quantity of sperm be 

 employed some agglutinating substance will remain free. 

 Whether we are dealing here with a true chemical union, 

 or merely with a process of adsorption is not yet 

 determined. 



If sperm suspensions are allowed to stand for some 

 hours they reach a condition where they will aggluti- 

 nate only with strong solutions. If the binding power 

 is then tested it is found that they fix as much of the 

 agglutinating substance as when fresh. The fixing 

 power of the sperm is thus entirely independent of its 

 capacity for being agglutinated, which depends upon 

 the freshness of the spermatozoa. The binding capa- 

 city would appear, therefore, to depend upon the pres- 

 ence of a certain substance borne by the spermatozoon 

 which we may call the agglutinable substance. We 

 may suppose that in stale sperm suspensions this sub- 

 stance may be cast off and lie free in the medium. 

 But this has not been actually determined. 



5 . " Hetero-A gglutination ' ' and Specificity 



The egg waters of Arbacia and of Nereis possess 

 substances each agglutinating for its own sperm. If 

 we test the Nereis egg water on Arbacia sperm we find 

 that it is entirely negative; if on the other hand we 

 test the Arbacia egg water on Nereis sperm the latter 

 is apparently strongly agglutinated. At first sight it 

 would seem that there is specificity in the one direction 

 but not in the other with reference to the agglutinating 

 substances. If, however, we examine the effect of the 

 Arbacia egg water on Nereis sperm more carefully we 

 find that the reaction bears quite a different character 



