50 THE INFLUENCE OF INANIMATE SURROUNDINGS. 



nutriment supplied to it, since it is fixed in the skin or in some 

 particular organ ; and moreover it must always perish if by any 

 circumstance the fluids which bathe its skin are so far altered 

 as to cease to be fit to nourish it. 



From these circumstances it will be at once understood that 

 there is a fundamental difference between true nutritive matters 

 and certain other substances. If indeed, as is sometimes done, 

 we choose to call everything food which may be in any way 

 concerned in digestion and the absorption of the gastric juice or 

 a partial conversion into organic substances, heat, and motion 

 irrespective of how or through what means the matters were 

 conveyed into the organism, and so rendered efficient we shall 

 be forced to apply the term not merely to oxygen and ozone, 

 which are taken into the body by respiration, or water and 

 salts, which are introduced in the most various modes often 

 through the skin but to all the other influences which are in- 

 dispensable to the life and growth of every individual. Kay, 

 even the sunbeams with their waves of heat and chemical light 

 must be included, for without their aid the stomach and in- 

 testines could not fulfil their functions, any more than the gills 

 or lungs, the brain or the organs of sense could carry on theirs 

 without healthy nutrition through the intestine. Hence we 

 are justified, while investigating the effects of nutrition on the 

 animal organism, in directing our attention solely to those in- 

 ternal organs of digestion which demand the collaboration of 

 external auxiliaries, and in leaving absorption by the skin quite 

 out of the question; for although this process, as regards its 

 effect on the life of the individual, acts precisely like the true 

 nutritive function, it induces no other connection with the ex- 

 ternal conditions of existence than those which subsist in all 

 animals through the skin and its relations to the medium 

 surrounding it, whether air or water, &c. These relations 

 never demand any special auxiliaries that depend on will, in- 

 clination, or disinclination, since the efficient action of the skin, 

 in all such cases, depends merely on the molecular relations 

 between it and the fluid matter with which it is in contact. 11 



The results we have so far arrived at may be thus shortly 

 recapitulated. We have seen that food, in the strict sense, 



