318 IMMUNOLOGY 



''that spermatozoa become very active when they reach the neigh- 

 borhood of an egg. ' ' Lilly has shown this to be a specific effect or 

 activation. When certain spermatozoa such as those of the Cali- 

 fornia sea urchin, Strongylocentrotus purpuratus, or of certain 

 annelids are put into sea water wliich has been in contact witli 

 the corresponding eggs, specific clumping or agglutination of the 

 spermatozoa occurs. 



Union of Egg and Sperm.— The fact that in fertilization, the 

 sperm enters the egg and only the eggs of the same or closely 

 related species, indicates not only specific invasive power on the 

 part of the sperm but also specific susceptibility on the part of 

 the egg for the same sperm. Toward the spermatozoa of other 

 species it exlnbits a general resistance. After fertilization witli 

 suitable spermatozoa has taken place the egg becomes immune to 

 invasion even by spermatozoa of the same species. 



Tvoeb calls attention to the similarity of fertilization or union 

 of sperm and egg to the phenomenon of phagocytosis. The sper- 

 matozoan enters through a protoplasmic process (fertilization 

 cone) wliich is comparable to the pseudopods of ameboid cells. 

 As a result of the entrance of the spermatozoan, in the case of 

 the sea urchins studied by him, the q^^ develops a membrane 

 which acts as a barrier to the entrance of any more spermatozoa. 

 This is obviously a specific defensive mechanism. Loeb has been 

 able to modify these various mechanisms, and to a large extent 

 control them by altering the salt content and pH of the sea water. 

 He concludes that the biological specificity in fertilization is 

 chemical in nature. 



Specificity and Genetics. — The exactness with which genet- 

 icists can predict the appearance of certain characters in the off- 

 spring of inbred strains of the grasshopper or white rat, plants, 

 etc., indicates that specific reactions are at work and that the 

 phenomenon of specificity is of broad biological significance. 



Production of Specific Hormones. — In the animal body specific 

 chemical substances such as thyroxin, insulin, cortin, adrenalin, 

 etc., are normal physiological products and each brings about 

 certain specific physiological reactions. The constancy of pro- 

 duction and the specificity of bacterial enzymes has long been 



