OCTOBEE 10, 1913] 



SCIENCE 



525 



urcHin, Arbacia, in sea water, wliicli causes 

 agglutination of the sperm of the same spe- 

 cies. The eggs of Nereis also secrete a sub- 

 stance having a similar effect upon its sperm. 

 I therefore named these substances sperm-iso- 

 agglutinins. During the present summer I have 

 ascertained that in the case of Arbacia, and 

 presumably also of Nereis, the agglutinating 

 substance is a necessary link in the fertilization 

 process and that it acts in the manner of an 

 amboceptor, having one side-chain for certain 

 receptors in the sperm and another for certain 

 receptors in the egg. As this substance rep- 

 resents, presumably, a new class of substances, 

 analogous in some respects to cytolysins, and 

 as the term agglutinin defines only its action 

 on sperm suspensions, I have decided to name 

 it fertilizin. 



My main purpose this summer was to study 

 the role of the Arbacia fertilizin in the fer- 

 tilization of the ovum. 



1. The Spermophile Side-chain. — The first 

 need in such a study was to develop a quanti- 

 tative method of investigation, and this was 

 done for Arbacia as follows: The agglutina- 

 tive reaction of the sperm in the presence of 

 this substance is, as noted in previous studies, 

 reversible, and the intensity and duration of 

 the reaction is a factor of concentration of 

 the substance. The entire reaction is so 

 characteristic that it was possible to arrive at 

 a unit by noting the dilution at which the 

 least unmistakable reaction was given. This 

 was fixed at about a five- or six-second reac- 

 tion, which is counted from the time that 

 agglutination becomes visible under a mag- 

 nification of about 40 diameters until its com- 

 plete reversal. The unit is so chosen that a 

 half dilution gives no agglutination of a fresh 

 1 per cent, sperm suspension. It was then 

 found that the filtrate from a suspension of 

 ' 1 part eggs left for ten minutes in 2 or 3 parts 

 sea water would stand a dilution of from 800 

 to 6,400 times, depending on the proportion of 

 ripe eggs and their condition, and still give 

 the unit reaction. Such solutions may then 

 be rated as 800 to 6,400 agglutinating power, 

 and it is possible, therefore, to determine the 

 strength of any given solution. This gives us 



a means of determining the rate at which eggs 

 are producing fertilizin in sea water. 



Determinations with this end in view 

 showed that the production of fertilizin by 

 unfertilized eggs of Arbacia in sea water goes 

 on for about three days and that the quantity 

 produced as measured by dilution tests dimin- 

 ishes very slowly. Such tests are made by 

 suspending a given quantity of eggs in a 

 measured amount of sea water in a graduated 

 tube; the eggs are then allowed to settle and 

 the supernatant fluid poured off and kept for 

 testing. The same amount of fresh sea water 

 is then added and the eggs stirred up in it, 

 allowed to settle, the supernatant fluid poured 

 off for testing, and so on. In one series run- 

 ning three days in which the quantity of eggs 

 was originally 2 c.c. and the total volume of 

 sea water and eggs in the tube 10 c.c, 6 to 

 8 c.c. being poured off at each settling, thirty- 

 four changes were made and the agglutinating 

 streng-th of the supernatant fluid diminished 

 from 100 at first to 20 at the end. Simultane- 

 ously, with this loss of agglutinating strength, 

 two things happen: (1) the jelly surrounding 

 the eggs undergoes a gradual solution; (2) the 

 power of being fertilized is gradually lost. 



It is obvious that the presence of fertilizin 

 in such considerable quantities in so long a 

 series of washings shows either (1) that solu- 

 tion of the jelly liberates fertilizin, or else (2) 

 that the eggs secrete more fertilizin each time 

 they are washed. Both factors enter into the 

 case inasmuch as (1) eggs killed by heat (60° C.) 

 will stand 14 or 15 such washings, but with 

 more rapid decline of agglutinating power than 

 the living eggs. The jelly is gradually dis- 

 solved away in this case also, and is presuma- 

 bly the only possible source of the agglutina- 

 ting substance. (2) Eggs deprived of jelly by 

 shaking continue to produce the fertilizin as 

 long as eggs with jelly, though in smaller 

 quantities at first, and they are equally capable 

 of fertilization. 



The fertilizin is therefore present in large 

 quantities in the jelly, which is indeed satu- 

 rated with the substance, but the eggs con- 

 tinue to produce it as long as they remain 

 alive and unfertilized. When the eggs are 



