24 ANIMAL BIOLOGY 



the materials of the body, involving the consumption of oxygen 

 and the liberation of carbon dioxide ; and further, that for a given 

 consumption of oxygen and liberation of carbon dioxide, about 

 the same amount of heat is produced by an animal as by a 

 burning candle. In other words, the oxidation of the complex 

 compounds which enter the body as food is definitely proportional 

 to the amount of energy which the body gives out, just in the 

 same way as the amount of work performed by a steam engine 

 and the amount of heat it liberates bear a strict proportion to its 

 consumption of fuel. 



This is an important discovery, because it goes far toward 

 establishing the fact that at least certain characteristic vital 

 phenomena are in accord with the laws which hold in the non-living 

 world. But the processes of metabolism are not so simple as per- 

 haps might be imagined from the results just mentioned. Heat 

 represents but one of the many energy transformations within the 

 organism, and biologists are at work trying to interpret one after 

 another in terms that are equally applicable in the realms of the 

 living and the lifeless. ' The symbol of the organism is the burning 

 bush of old." 



One naturally asks whether living matter possesses some special 

 form of energy — 'vital force' — which is quite different from 

 chemical and physical energy. This is the philosophically impor- 

 tant question of vitalism. From the standpoint of biology we 

 may say that no instrument ever devised has detected such en- 

 ergy, and until some unique vital energy can be made evident to 

 one of the human senses, it does not fall within the scope of science 

 — science can neither deny nor affirm its existence. Perhaps for 

 the present it is sufficient to realize that unique phenomena may 

 emerge from new relationships — relationships change the prop- 

 erties of things. The properties of molecules are those which the 

 atoms have when they are in the molecule, and the phenomena 

 of life depend on — emerge from — the physico-chemical con- 

 stituents of protoplasm when, and only when, they are in proto- 

 plasm. A living cell exhibits "many unpredictable properties be- 

 yond those of the mere sum of its individual constituent molecules 

 and compounds, or the additive resultants to be derived from any 

 arrangement of them." 



However, it is important to note that many of the grosser phe- 

 nomena of life are being gradually restated in terms of the physical 



