THE CONSERVATION OP ENERGY AND GKOWTH 227 



That is of benefit primarily in order to acquaint the individual 

 living unit with, on the one hand, its closeness to food-stuffs, or, 

 on the other hand, with the presence of physical or other agents 

 deleterious to the organism. Assimilation and excretion are 

 but the auxiliaries in the due utilization of materials which aid 

 growth, and in removing from the organism all materials whose 

 continued presence would disturb the process. Growth, then, 

 is the central or essential phenomenon of life, and to understand 

 life it is necessary that one gains a clear idea of what is the 

 essential nature of this process of growth. 



Let us then consider what growth means. It means quantita- 

 tive increase in the individual matter endowed with life, increase 

 in the living substance. That individual may consist of a single 

 cell, may be an almost infinitesimal micrococcus, for example, or, 

 at the other pole, say in the elephant or in the whale, may consist 

 of a huge aggregate of countless billions of cells, all associated 

 and depending the one upon the other. In this latter case it is 

 the separate cells which, some or all of them, increase in size, 

 and with this increase also in number. Each cell of such a 

 multicellular organism is, we know, derived from a primitive 

 fertilized ovum by repeated division of the original single cell ; 

 and in this process of division there is a partition of the bioplasm, 

 of the vital matter. During the period of most rapid growth, 

 in the stage of development, this increase in size of the individual 

 cells and their multiplication is most rapid, and when we compare 

 the adult with the ovum from which it sprang, when we know 

 that in suitable environment, a single bacillus, for instance, 

 dividing, can, in twenty-four hours, give rise to hundreds and 

 thousands, not to say millions of bacilli equal in size and identical 

 in properties to the original bacillus — one observer has estimated 

 that in the breeding of the unicellular Rotifer, if all the possible 

 progeny could be preserved, there "would in the course of a year 

 be developed a mass of organic living matter as large as this 

 world of ours — we can have no doubt, not merely that growth 

 means a heaping up, through the agency of the essential vital 

 portion of the protoplasm, of secondary substances, not in 

 themselves living and vital, but that that living matter itself is 

 marvellously increased in amount. There is no other possibility 

 open to us. But now, can we picture to ourselves the nature 

 of such increase in the vital substance, the actual bioplasm ? 



