THE FERTILIZATION-REACTION 



it may suggest that the initial stage in the reaction between 

 egg and spermatozoon is the agglutination of spermatozoon 

 to egg-substance. The agglutination here discussed is 

 never induced by treating spermatozoa of one species with 

 sea-water charged with the sperm-agglutinin from eggs of 

 another. This, hetero-agglutination, offers a different pic- 

 ture qualitatively and quantitatively and is due to a sub- 

 stance in the body-fluid.^ Thus fertilizin, as indicated by 

 the agglutination-reaction which it induces, is specific. 



No question in the whole problem of fertilization has 

 more profound significance than this of specificity. Fre- 

 quently students of fertilization have asked themselves the 

 question: how is it that in the sea, eggs of one species are 

 fertilized by specific and not by foreign spermatozoa t In 

 other words, how do eggs maintain fertilization-specificity? 



In the laboratory fertilization by foreign spermatozoa 

 of most marine eggs almost never occurs as a normal event. 

 If one mixes eggs of a sea-urchin and of a worm and insemi- 

 nates them with spermatozoa of either sea-urchin or worm, 

 only specific fertilization occurs. Also, a mixture of two 

 kinds of spermatozoa added to eggs belonging to only one 

 species of them induces species-fertilization. It has gen- 

 erally been found that before cross-fertilization takes place 

 among sea-urchins, starfishes, etc., the eggs need either a 

 previous treatment with alkali or heat, or long residence 

 in sea-water, so that they become "stale," or an insemina- 

 tion with an excessive number of spermatozoa. All these 

 methods for inducing cross-fertilization can be shown to 

 injure the egg-surface, and so to decrease the egg's vitality. 

 As long as the integrity of the ectoplasm remains unim- 

 paired, cross-fertilization fails. 



Specificity in fertilization closely resembles that in immu- 

 nity-reactions, where a specific anti-toxin combines with 

 specific toxin. It is far more specific than an enzyme- 



^ Just, igigb. 



IQ7 



