616 



JOHN R MUKLIN 



fertilized eggs, lends weight to the view that oxygen is in some way essen- 

 tial to the growth process, but his further observation that there was no 

 proportion between the amount of oxygen absorbed and the number of 

 nuclei (blastomeres) present, and that still more oxygen was absorbed 

 when the eggs were placed in hypertonic solutions and cell divisions had 

 ceased (Warburg(fr)), certainly do not favor the idea that oxygen absorp- 

 tion is dependent upon nuclear activity. This is in accordance with Kub- 

 ner's(w) view that the morphological changes in the nucleus accompanying 

 cell division are the expression of synthetic processes rather than of the de- 

 structive processes of oxidation. 



Bayliss(&) explains the chemical process of oxidation in the cell as fol- 

 lows : "Some autoxidizable substance in the cell takes up- molecular oxy- 

 gen, with the formation of peroxids and activation of half the oxygen. The 

 other half of the oxygen serves for complete oxidation of part of the 

 autoxidizable substance. These peroxids are acted upon by peroxidase, 

 with further increase of active oxygen, which is able to bring about oxida- 

 tion of substances not autoxidizable and otherwise difficult of oxidation." 

 The structure of the cell, however, also plays a part. For example, ac- 

 cording to Warburg (c), in a muscle cell a much larger part of the chemical 

 energy appears as free energy than if the cell is disintegrated. The ar- 

 rangements within the cell which we call cell structure "in some way catch 

 the chemical energy of the oxidation processes before it has fallen to the 

 state of free heat." It is by such arrangements or structure that the work 

 of a contracting, a secreting, an absorbing cell, etc., is carried on. 



Even in cells which do no external work or osmotic work, however, 

 structure is important for oxidation. Thus, in the unfertilized eggs of the 

 sea urchin, Warburg and Meyerhof have shown that the addition' of iron 

 salts increases oxidation very perceptibly. Salts of no other metal do this. 

 Iron, in other words, is a catalyst for oxidation. Now the significance of 

 structure (alveolar, if we please), as Warburg sees it, is just this, that it 

 affords surfaces for the condensation of the catalyst and thereby puts it to 

 work. 



But why should energy be set free in cells that do no work ? Warburg's 

 answer to this is that the liberation of energy by oxidation preserves the 

 structure, or the integrity, if one will, of the living substance. If cell 

 constituents are to be prevented from mixing freely, diffusion surfaces 

 must be maintained, and the maintenance of their semi-permeable prop- 

 erties calls for a certain difference of electric charges which can only be 

 kept up by the liberation of energy from some source. Hence it is that 

 all living substance must respire and must liberate a certain amount of free 

 heat. The maintenance of a constant temperature would, on this view of 

 the matter, be a fundamental property for cells whose structure could be 

 maintained only by a certain rate of energy release (see page 602). 



2. Metabolism of Embryonic Growth (Murlin(c)). Development oe- 



