FXEMENTARY PROBLEMS IN PTTYSIOLOCi Y. 425 



ciple that Hviiii? material acts by virtue of its stiuctiire, provided that 

 we allow the term structure to be used iu a seuse which carries it be- 

 yond the limits of anatomical investigation, i. e., beyond the knowledge 

 which can be attained either by the scalpel or the microscope. We 

 thus (as I have said) proceed from function to structure, instead of the 

 other way. - - - 



At present the fundamental questuHis in physiology, — the problems 

 which most urgently demand solution, are those which relate to the 

 endowments of a])i);nently structureless living matter, and the problem 

 of the future will be the analysis of these endowments. With this 

 view, what we have to do is first, to select those cases in which the vital 

 pro(;ess offers itself in its simplest form, and is consequently best under- 

 stood; and secondly, to inquire how far in these particular instances 

 we may, taking as our guide the principle I have so often mentioned as 

 fundamental, viz, the correlation of structure with function, of mech- 

 anism with action, proceed in drawing inferences as to the mechanism 

 by which these vital processes are in these simplest cases actually car- 

 ried out. 



The most distinctive peculiarity of living- matter, as compared with 

 non-living, is that it is ever changing while ever the same, i. e., that life 

 is a state of ceaseless change. For our present purpose I must ask 

 you, first, to distinguish between two kinds of change which are equally 

 characteristic of living organisms, namely, those of growth and decay 

 on the one hand, and those of nutrition on the other. Growth, the 

 oiologist calls evolution. Growth means the unfolding, ?'. e., develop- 

 ment of the latent i)otentialities of form and structure which exist in 

 the germ, and which it has derived by inheritance. A growing organ- 

 ism is not the same to-day as it was yesterday, and consequently not 

 quite the same now as it was a minute ago, and never again will be. 

 This kind of change I am going to ask you to exclude from considera- 

 tion altogether at this moment, (for iu truth it does not belong to 

 Physiology, but rather to Morphology,) and to limit your attention to 

 the other kind which includes all other vital phenomena. I designated 

 it just now as nutrition, but this word expresses my meaning very in- 

 adequately. The tern) which has been used for half century to des- 

 ignate the sum or complex of the nondeveloi)mental activities of an 

 organism is " exchange of material," for which Professor Foster has 

 given the very acceptable substitute metabolism. INIetabolism is only 

 another word for "change," but in using it we understand it to mean 

 that although an organism in respect of its development may never be 

 what it has been, the phases of alternate activity and repose which 

 mark the How of its life-stroam are recurrent. Life is a cyclosis in 

 which the organism returns after every cycle to the same point of de- 

 parture, ever changing — yet ever the same. 



It is this antithesis which constitutes the essential distinction between 

 the two great branches of biology, the two o})posite aspects in which 



