STUDIES OF FERTILIZATION 571 



The same result was obtained in other experiments and I could 

 find no evidence that blood decreased the delicacy of the aggluti- 

 nating reaction. 



If then the fertilizin is essential for fertilization, and if the 

 inhibitor in the blood does not operate by preventing union of 

 this substance with the sperm, it follows that another side-chain 

 of the fertilizin capable of being occupied by the inhibitor is also 

 operative in fertilization. There must be action of the fertilizin 

 on the egg as well as on the sperm, and hence we may assume an 

 ovophile as well as a spermophile side-chain of the fertilizin, and 

 the inhibitor must act by occupying the former. 



Now Robertson ('12) has stated that various proteins when added 

 to the sea-water can be shown to inhibit membrane formation by 

 sperm, though as a matter of fact his experiments demonstrate such 

 a result only for ovomucoid in concentrations above 0.25 per cent. 

 It might therefore be supposed that the inhibiting effect of blood 

 of the same species was only a special case of protein inhibition. 

 There are, however, considerations that show such a view to 'be 

 untenable. (1) As already shown the degree of inhibition by 

 undiluted blood ranges all the way from zero to 100 per cent; 

 and we cannot suppose that the amount of protein in the blood 

 of different individuals varies to the extent required to explain 

 such an extraordinary difference. (2) In the second place the 

 mode of neutralizing the inhibitor, as shown below, involves 

 an enormous increase of colloid content of the blood, for it con- 

 sists in saturating the blood with fertilizin and dissolved jelly; 

 the blood may thus become actually syrupy in consistency 

 and yet have no inhibiting effect on fertilization. (3) I have 

 tested the effect of egg-albumen in the sea-water up to 0.15 per 

 cent without finding any inhibition of fertilization. Of course 

 in higher concentrations a certain degree of inhibition may 

 occur. However the reasons given under 1 and 2 above, certainly 

 exclude the idea that we are dealing with an effect common to 

 colloids in general, which must be assumed to operate through 

 changes in the membrane. It is necessary to assume some spe- 

 cific substance acting as inhibitor. 



THE JOURNAL O* EXPERIMENTAL ZOOLOGY, VOL. 16, NO. 4 



