84 RALPH S. LILLIE. 



to perform the work of chemical and structural synthesis. En- 

 zymes may facilitate or direct certain kinds of combinations, 

 and in this way they may be important as accessory factors in 

 the constructive process ; but the essential controlling factors are 

 evidently of a more active, i. e., work-performing, kind. And 

 since these factors vary in their activity with function, it follows 

 that the conditions controlling the degree and rate of functional 

 activity i. e., generally speaking, the conditions of stimulation 

 must at the same time be the conditions controlling the specific 

 constructive processes. 1 It is true that construction does not 

 always run parallel with destruction, the rate of which may often 

 temporarily exceed that of repair; and at times nutritive or other 

 conditions may render complete replacement impossible; or at 

 other times construction may preponderate, as in growth. 

 Nevertheless an interdependence of the kind indicated unques- 

 tionably does exist; and apparently we must infer that part of 

 the energy freed in the oxidation (or other energy-yielding decom- 

 position) which performs the work of function is applied, in some 

 manner as yet unknown, to build up the material required for 

 maintenance or further growth. 



If we adopt this general hypothesis, we must reject as entiiely 

 insufficient the conception of growth as being analogous to a 

 process of crystallization, or as being determined by syntheses of 

 the enzymatic kind ; and we are led to look for some other type of 

 process in which the formation and deposition of structural 

 material is controlled by energy set free in chemical change. 

 This process must be capable of variation in rate, of interruption 

 and renewal, and of reversal, if it is to correspond to such 



1 This is indicated by Bernard s already cited observation that anaesthetics 

 arrest growth-processes reversibly in the same manner as they inhibit stimulation 

 or other forms of functional activity, a fact suggesting that physico-chemical 

 changes of the same nature control both growth and the response to stimulation. 

 If this is true, it seems probable that the structures primarily concerned in stimu- 

 lation are also those primarily concerned in construction, i. e., the site or locus of 

 both constructive and destructive processes is the same, the two representing 

 reverse phases of the same process. On such a view the idea that special regions 

 of the cell (e. g., the nucleus) are the exclusive seat of syntheses would have to be 

 abandoned. There is, however, much evidence that the nucleus is necessary for 

 the continuance of synthetic processes; possibly it gives rise to certain substances 

 which are required for the maintenance of the structures more immediately con- 

 cerned in the specific syntheses. 



