SEVENTH ANNUAL MEETING 35 



are incapable of fertilization ; after it is lost, whether by wash- 

 ing 1 or preceding fertilization, the capacity for fertilization is 

 also lost. We therefore conclude that the agglutinating sub- 

 stance is necessary to fertilization. 



II. Use of Inhibitors. 



1. Inhibitors in blood. 



It is a fact well known to Embryologists, but hitherto not 

 studied in any systematic fashion, that the plasma of blood or 

 tissue secretions of the species tends to hinder the fertilization 

 reaction. 



I have made a somewhat detailed study of this phenomenon 

 in the case of the Sea-Urchin, Arbacia punctulata, the detailed 

 results of which are published in volume 16, of the Journal of 

 Experimental Zoology. Here it may suffice to say that the 

 addition of filtered serum of Arbacia blood to the sea-water 

 in which insemination is to be performed, strongly inhibits 

 fertilization. If a series of blood solutions containing, let us 

 sayi 10, 20, 30, 40 per cent, etc., up to 100 per cent blood be 

 prepared and equal quantities of ova inseminated with equal 

 quantities of spermatozoa in each member of the series, the 

 per cent of fertilization will usually run from about 100 per 

 cent in fertilization control to zero in the undiluted blood 

 serum. All the sperm are living and active in each member of 

 the series. 



The inhibition by the blood is not due to direct harmful 

 action on either reproductive element alone for either eggs or 

 spermatozoa may be exposed to the action of such solutions 

 and after washing be found to possess good capacity for fertili- 

 zation. It might be supposed that the inhibitor acts like the 

 anti-fertilizin by preventing union between fertilizin and sperm- 

 atozoa. This is, however, not the case because of a solution of 

 fertilizin in blood is as effective in agglutinating spermatozoa 

 as a similar solution in sea-water. 



A second hypothesis would be that the inhibitor might act 

 on a second side-chain of the fertilizin which is active in fer- 

 tilization by combining with certain constituents of the ovum. 

 If this is the case it would follow that the inhibitor in the blood 

 could be neutralized by first saturating it with fertilizin from 

 other eggs and this is found to be the case : If a given sample 

 of blood be divided into equal parts of which one is saturated 

 by fertilizin from unfertilized eggs, and inseminations be 

 made in graded series of both, the usual inhibition reaction will 

 be found in the first series, but is entirely absent in the second 

 series. 



