ISO L. V. HEILBRUNN. 



swelling of the membrane varies with the season. In the height 

 of the season only quite concentrated sperm suspensions produce 

 the phenomenon. But towards the end of August, as the season 

 begins to wane, more and more dilute suspensions become ef- 

 fective, until at the very close of the season, it is difficult to 

 secure true membrane elevation at all. Probably the fluid 

 emitted with the sperm is then charged with the substance which 

 causes the swelling. 



In the preceding section it was shown that sea-urchin blood 

 retards acid membrane swelling, but favors salt membrane swel- 

 ling. This fact makes it possible to determine the general 

 nature of the membrane swelling produced by sperm. One 

 has only to observe the action of concentrated sperm suspensions 

 in the presence of blood. If blood favors the swelling, this can 

 be taken as evidence that the sperm action is similar to that of 

 salts, if on the other hand it retards swelling, an acid is probably 

 responsible. On July 7, 1914, 5 c.c. of sea-water plus 9 drops 

 of egg suspension plus 5 drops of "dry" sperm were mixed in 

 Syracuse watch-crystal A. Watch-crystal B contained 4 c.c. 

 of blood (filtered from cfs and 9s) plus 9 drops of egg sus- 

 pension plus approximately the same amount of sperm as did 

 A. Both watch-crystals were shaken slightly to insure mixing. 

 In A, the membranes swelled gradually; after 43 minutes they 

 measured approximately 2p. In B, on the contrary, no membrane 

 swelling could be observed. 



It might be objected that in the above experiment the blood 

 had some effect which prevented intimate contact of sperm 

 with egg. This objection is obviated by the following experi- 

 ment. It was performed at the very close of the season, at a 

 time when as previously pointed out, sperm suspensions have a 

 much greater tendency to produce swelling. On September I, 

 1914, considerable difficulty was experienced in procuring sperm. 

 Ten males were cut open and allowed to shed (several others had 

 been rejected as being totally incapable). Of these ten, only 

 two shed any sperm at all, and this was rather watery. Pre- 

 liminary experiments showed that when 3 drops of this watery 

 "dry" sperm were added to about 10 c.c. of sea-water and about 

 8 drops of the resulting suspension were again diluted with 10 

 c.c. of sea-water, a suspension was obtained which caused mem- 



