MEMBRANE-FORMING AGENTS 459 



which is confined to the cortical layer of the egg. The formation of the 

 membrane is accompanied by a very manifest increase in the volume 

 of the egg which can only be accounted for by an imbibition of water. 

 The cytolysis which succeeds membrane-formation is accompanied 

 by a still greater swelling and imbibition of water. This has been 

 attributed by Loeb and von Knaffle-Lenz to the partial liquefaction or 

 destruction of an Emulsion-structure within the cell or at its periphery. 

 We have seen (Chapter XIII) that protoplasm consists of an 

 emulsion of lipoids in a protein medium and that this emulsion 

 must be particularly concentrated at the surface of the protoplasm 

 owing to the lowering of interfacial tension which is thus brought about. 

 Any increase in the diameter of the lipoidal droplets in this superficial 

 layer, or their coalescence, must lead to a corresponding increase in 

 the width of the interstices between them, and hence to an enhanced 

 permeability for water and salts. The fat-dissolving character of the 

 majority of the cytolytic agents is thus the origin of the taking up 

 of water by the egg which results in the physical phenomena of cytoly- 

 sis or cell-liquefaction. Any other agent which will induce imbibition 

 of water will, however, also bring about cytolysis. For example 

 distilled water or Hypotonic Solutions bring about cytolysis because 

 the excess of osmotic pressure within the egg forces water into the cell 

 even through the normally narrow interstices of the cortical layer. 

 Other agents may induce cytolysis by altering the solubility of the 

 protein component of the emulsion, and hence cytolysis may be induced 

 in certain cells by physiologically unbalanced salt solutions. Even 

 membrane formation, as Lillie has observed, may be brought about in 

 certain echinoderm eggs (Arbacia) by exposing them to pure solutions 

 of certain Sodium Salts, and this effect is inhibited by an admixture 

 of Calcium Chloride. 



The formation of the fertilization-membrane, therefore, which is 

 the first step in the stimulation of development which constitutes 

 fertilization, is essentially a partial and arrested cytolysis. The impor- 

 tant question now presents itself, in what way does this partial 

 cytolysis affect the chemical processes of the cell? 



One very decided effect of fertilization by spermatozoa is enhance- 

 ment of Basal Metabolism, indicated by a greatly increased consump- 

 tion of oxygen. The following measurements by Loeb and Wasteneys 

 illustrate this fact: 



CONSUMPTION OF OXYGEN BY A GIVEN MASS OF ARBACIA EGGS. 



Mg. of oxygen consumed 

 Time. per hour. 



Before fertilization , . . . .0.24 



First hour after fertilization 0.94 1 



Second hour after fertilization 0.80 



Third hour after fertilization 0.87 



Fourth hour after fertilization 0.91 



Fifth hour after fertilization . . 1.05 



1 This value is too high, owing to the presence of sperm which were washed away 

 before the next determination was made. 



