NORMAL PROCESSES OF ENERGY' METABOLISM 615 



ing the woman, tiat is, as a man of the same size) the actual heat production 

 is generally lowor than the theoretical. Larger women show a relatively 

 larger deficiency than smaller ones and the suggestion is made by the 

 authors that the hody weight is the primary factor in determining the de- 

 ficiency. <4 The most critical test shows that when body weight, stature, and 

 age are taken into account, women show about G.2 per cent lower metab- 

 olism than men." 



D. Energy Metabolism of Growth 



1. Differences between Growth and Maintenance. The chemical proc- 

 esses by which the living substance is maintained are not identical with 

 those by which it was originally produced. For example, growth and 

 division of the nuclei are essential in the production of new tissues, while 

 the mere replenishment of cell materials, such as is taking place continu- 

 ally on a small scale or such as may take place in convalescence on a large 

 scale, may go on without division of the nuclei. Since it is known that 

 the nucleus is essential to processes of intracellular digestion (Verworn), 

 it is possible that the nucleus plays some essential role in this process of 

 replenishment; but the fact that the nucleus itself does not grow and divide 

 under these circumstances (Loeb, J.(&)), together with the fact that its 

 reactions and constitution are kno\vn to be different from those of the cyto- 

 plasm, makes it very probable that growth involves chemical processes not 

 concerned in the replenishment which follows ordinary waste or that which 

 follows extraordinary whste in diseased conditions. Rubner(rc) has 

 drawn attention to the fact that the maintenance tendency is of primary 

 importance even in the young organism, since the "wear and tear" quota 

 (Abnutzungsquote) must be satisfied before growth (postcmbryonic) of 

 the organism as a whole can assert itself. If we assume that the every- 

 day repair concerns mainly the cytoplasm, except where cells are actually 

 being destroyed, Ruhner's view might be interpreted to mean that the 

 processes in the nucleus which result in its growth and division can take 

 place, even in the young organism, only under certain optimum nutritive 

 conditions of the cytoplasm. 



There is no reason for thinking that the mechanism by which energy 

 is liberated in young cells is different from that which performs the same 

 service in mature cells. The living substance of all cells (with the ex- 

 ception of the anaerobic forms) is dependent upon some power, call it the 

 "activation of oxygen/ 7 whereby oxygen becomes capable of uniting with 

 the elements of the soluble foodstuffs at a temperature much below the 

 ordinary kindling temperature. 



Warburg's (a) recent observation that fertilized sea urchin eggs absorb 

 six to seven times as much oxygen in the same length of time as do un- 



