II. ONTOGENY 359 



A number of facts have been found that striking disturbances are 

 raised in the egg cell following the fertilization like in super-cooled 

 water or in super-satui'ated solution to which vigorous shaking is ap- 

 plied. Thus, unfertilized egg behaves like a cell in a "latent" state, 

 all the metabolic exchanges being extremely slow, but on the fertili- 

 zation they are suddently elevated. This may chiefly be attributed to 

 the temporary liberation of polar groups. It should be remembered 

 that a protein molecule in a metastable state will change into a stable 

 state if a suitable stimulus is provided to initiate the change, and 

 that at the first stage of the change the protein molecule is to be un- 

 folded with the temporary liberation of free polar groups. 



On the one hand, as was previously stated, the combination be- 

 tween proteins and lipids in the protoplasm becomes occasionally loose 

 when the protoplasm structure is disturbed by the infection with a 

 virus. On the other hand, it has been reported that lipids which can- 

 not be extracted from unfertilized egg become easily extractable fol- 

 lowing the fertilization (32), It has been claimed, however, that a 

 part of cephalin will combine firmly with protein after the fertili- 

 zation (33) ; this may depend upon the liberation from the protein of 

 polar groups capable of combining with cephalin. Such a liberation 

 of free groups may cause the mutual association of proteins leading to 

 the coagulation, which has been observed with eggs of the sea urchin 

 to begin three minutes after insemination, obtaining its maximum in 

 seven minutes, and being maintained thereafter unchanged for two 

 hours (19). If the eggs of the sea uixhin are frozen at —77° C. and 

 then desiccated at —25° C, one obtains a fine powder that may be 

 extracted at low temperatures with KCl solution at pH 7.3. Under 

 this condition, 82 to 85 per cent of the proteins from the unfertilized 

 egg dissolve, while for the fertilized egg this becomes 69 to 72 per 

 cent (19). A portion of the egg proteins, more than 10 per cent of the 

 total protein, thus becomes insoluble at the time of fertilization, 

 presumably because of the mutual combination or the coagulation of 

 the proteins due to the liberated polar groups. 



It is generally known that a variety of enzymes are activated 

 following fertilization. This activation may be attributed to the liber- 

 ation of active enzymatic structures due to the disturbance by the 

 sperm. During the coagulating process of blood a series of enzymes 

 or enzyme-like factors are successively produced as stated in the last 

 Chapter of Part IV. In the protoplasm of the egg the situation may 

 become the same on the fertilization as in the coagulating blood plasm. 



Serum protease, also known as plasmin and fibrinolysin, has been 

 shown to be present in an inactive state as a natural constituent of 

 mammalian blood. Numerous activating agents have been recorded 



