214 THE MECHANISM OF LIFE 



of the gland, osmotic changes, chemical reactions, and so on. These 

 things do not explain the secretion of saliva : they only describe it. 

 An explanation would place beneath blood-pressure, chemical 

 reactions, etc., some simple irreducible concepts, just as in the 

 ' planetary theory we place beneath the complex motions of planets 

 and satellites (which correspond logically to the molecular move- 

 ments occurring in the tissues of the gland) the law of gravitation. 



It is, perhaps, not easy for the non-professional reader to 

 appreciate this point. It seems natural to suppose that, because 

 chemical and physical reactions are all that we can study scien- 

 tifically in the living animal body, these things explain life. They 

 only describe life : they are the physical expressions of the activities 

 of the organism. Investigation itself is not primarily speculative, 

 but is rather something useful. Just as the submaxillary gland 

 — and all the other parts of the body that enable it to act — 

 function so as to produce a liquid that digests certain foodstuffs, 

 so the mental mechanism that we call the categories of the under- 

 ^standing functions so as to do something that (like the production 

 of a ferment) is useful to the organism. In the higher races of 

 man it has become speculative also, but even there it is pre- 

 dominantly practical, and (as Bergson shows) is therefore 

 hampered when its aims are purely speculative. 



Let the reader reflect on all this, and he will certainly see that 

 physiology has never explained life activities, but has only 

 described them, and that indeed is the glory of the science, for 

 the description has given us (or will yet give us) the mastery over 

 inimical nature. Let him examine the attitude of the " ordi- 

 nary " man — that is (say), some nine-tenths of all those who are 

 capable by prolonged study of following the methods and results 

 of scientific investigation. This ordinary man will almost 

 certainly ask, What is it for ? He will expect that investiga- 

 tion ought to have some useful result, and he will probably be 

 unable to conceal his disappointment (or even contempt) when 

 he learns that the result is only an increase in abstract knowledge ! 



Life activity therefore expresses itself in physical and chemical 

 phenomena, but physical and chemical reactions do not " ex- 

 plain " life — that is the result to which we seem to be led. 



Life and Energy. — In seeking for the explanation we have, 

 therefore, to find some concept which will be special to the 

 phenomena which we call vital ones, and which need not be 

 required when we investigate and explain inorganic happenings. 



