SPERM AGGLUTINATION AND FERTILIZATION. 3 1 



occurence of such reactions, taking place, as they must, across 

 the egg membrane, is dependent on physical conditions of the 

 membrane, especially its permeability to the substances con- 

 cerned. In speaking, as I did, of five blocks to the fertilization 

 reaction, I was concerned only with the chemical reactions in- 

 volved. There may be other blocks of a physical nature. 

 Indeed these were much in evidence in the fertilization of Asterias, 

 which I studied in the first part of the summer, and shall report 

 on elsewhere. Another important consideration is that the 

 reaction must also be dependent on environmental conditions 

 such as temperature, ionic constitution of the medium (see Loeb,- 

 '14&), etc. Blocking of fertilization may also arise from such 

 causes. 



Continuing the exposition of the theory; I identified the fertil- 

 izin of Arhacia with the substance found in the fluid of egg sus- 

 pensions which causes agglutination of sperm suspensions of the 

 same species. This phenomenon cannot possibly be lacking in 

 significance, for it furnishes direct evidence of a combination of 

 egg and sperm derivatives; the phenomenon itself is not con- 

 cerned in fertilization, for a single spermatozoon may fertilize 

 an egg. Neither does the absence of such agglutination in other 

 species affect in the least the conclusion that may be drawn from 

 Arhacia: because we may have a combination of egg and sperm 

 derivatives without any sperm agglutination. The agglutination 

 is incidental, the combination is the essential thing. 



The fertilizin theory in its essential aspects is not dependent 

 on the identification of fertilizin and sperm agglutinating sub- 

 stance. I believe in their identity; but if it were proved, as 

 Loeb has sought unsuccessfully to do, that the agglutinating 

 substance is not essential for fertilization, the fertilizin theory 

 would still not be attacked in its essence. The conception that 

 initiation of development is essentially a phenomenon of activa- 

 tion would still stand in opposition to theories of external agents 

 acting directly by corrosion (cytolysis), or coagulation, or what 

 not. The egg could still be regarded as a self-contained system 

 with no more than the usual environmental relations. It is only 

 from this point of view that the complex phenomena of parthen- 

 ogenesis and fertilization can be united in a logical whole. 



