460 PROCESSES INFERRED FROM INDIRECT OBSERVATION 



During the period occupied by the experiment the eggs had pro- 

 ceeded to the thirty-two cell stage. The rate of oxidations does not 

 reach its maximum instantaneously, but increases progressively. For 

 example, Warburg in comparing the rates of oxidation in the 8-cell and 

 32-cell stages found that they were in the ratio of 4.2 to 6.8. 



Corresponding with these facts we find that deprivation of oxygen 

 arrests the processes of development and prevents nuclear and cell- 

 division. The same effect is brought about by Cyanides, which also 

 arrest cellular oxidations and, in multicellular animals, act primarily 

 by reducing tissue-respiration. It is possible to show, however, that 

 other processes besides oxidations are initiated by fertilization, for 

 when the fertilized eggs of Strongylocentrotus purpuratus are left in 

 sea- water free from oxygen for twenty-four hours at 15 C. they will 

 not develop during that time, but they will begin to develop at once 

 if oxygen is admitted. It is found, however, that their development is 

 no longer normal, since they form abnormal blastulse and never or 

 rarely reach the gastrula stage (Loeb). If unfertilized eggs are kept for 

 twenty-four hours without oxygen they remain uninjured, and upon the 

 addition of sperm they develop normally and produce healthy plutei. 

 The same result is obtained if development is arrested by potassium 

 cyanide. 



It has been shown by Loeb in fact that not only is development 

 arrested by deprivation of oxygen, but it is also, to some extent, 

 reversed. Thus if development be initiated by membrane-formation 

 with butyric acid in Arbaeia eggs, on restoring the eggs to normal sea- 

 water they die within a few hours unless they are treated with hyper- 

 tonic sea-water; moreover, they are no longer fertilizable by sperm. 

 However, if, instead of transferring the eggs to normal sea-water, 

 they are placed in sea-water containing sodium or potassium cyanide, 

 or chloral hydrate, then after some hours they no longer die when they 

 are returned to normal sea-water and, in fact, may now be fertilized 

 by sperm. 



The fact that Chloral Hydrate and other narcotics, as well as cyanides, 

 will arrest the development of fertilized eggs is a striking proof, in 

 itself, that other chemical phenomena besides oxidation underlie 

 development, for the narcotics, although they suppress or retard the 

 processes of cell division and development do not perceptibly diminish 

 the rate of oxidation in the egg. The acceleration of basal metabolism 

 which occurs in fertilization, therefore, although essential to develop- 

 ment, is not the only essential chemical transformation which underlies 

 the process of development. The vast majority of the reactions which 

 occur in living tissues are oxidations, reductions, or hydrolyses 1 and 

 we may therefore consider it probable that Hydrolysis also occurs and 

 performs an essential function in early development. 



It remains now to discuss the relative parts played by the two 

 factors of fertilization, the one consisting in the partial cytolysis of the 



1 Decarboxylization should perhaps be added to this list. Deaminization may with 

 propriety be classed among the hydrolyses. 



