VITAL EXPENDITURE 259 



tte material with, whicli it replaces its depleted stock. The 

 " ingesta " of the organism balance its " excreta." Albumin, 

 sugar, fat, oxygen, balance quantitatively the water, carbonic 

 acid, and urea which are their waste matters. The energy mani- 

 fested by the organism in all vital phenomena — ^which has its 

 source, as we have seen, in the chemical energy derived from 

 the nutritive substance — may be measured as a quantity of 

 heat. That is to say, the vital energy brought into action is 

 restored to the outer world as heat ; which amounts to saying 

 that the chemical phenomenon is the source of all vital energy, 

 and the thermal phenomenon its resultant. Thus, the chemical 

 energy which the nutritive substance is capable of imparting to 

 the organism constitutes the alimentary potentiality of that 

 substance, its dynamic value. And this dynamic value is also 

 its vital value ; for, as we have seen, the chemical energy liberated 

 by the digestion of the nutritive substance is destined to manifest 

 itself in the physiological activities of the organism.^ 



Organic life is thus impossible without expenditure ; that ex- 

 penditure is expressed by the quantity of physiological work 

 that can be performed under given circumstances ; and the 

 health of the organism depends upon its physiological work 

 corresponding to the chemical energy derived from its food — 

 in a word, on its activity being normal. A diet which is defec- 

 tive will possess a correspondingly reduced vital value — that is 

 to say, the physiological activity will be correspondingly 

 reduced. But, on the other hand, a diet which is excessive 

 will be equally harmful, for it will provoke a hyperactivity of 

 the functional system which is altogether out of proportion 

 to the potential strength of the organism ; for every organism 

 can but perform the work for which it is naturally fitted. Thus 



<■ The formation of new protoplasm requires a considerable amount of 

 energy, for the chemical composition of protoplasm is very elaborate. 

 It is probable that the energy liberated by the digestion of the mitritive 

 substance supplies the needs of the organism in this respect. 



17—2 



