Page:Life and death (1911).djvu/133

 *logist and medical man who attempted it had failed, and this for various reasons.

The general cause of this failure was that most definitions, popular or technical, interposed the condition that the food must be introduced into the digestive apparatus. "It is," said they, "a substance which when introduced into the digestive tube undergoes, etc., etc." But plants draw food from the soil, and they possess no digestive apparatus; many animals have no intestinal tube; and in the case of certain rotifera, the females possess a digestive apparatus, while the males have none. Nevertheless all animals feed.

On the other hand, there are other substances than those which use the digestive tract for the purpose of entering the organism, and which are eminently useful or necessary to the maintenance of life. In particular we may mention oxygen.

The distinctive feature of food is its utility—when conveniently introduced or employed—to the living being. Claude Bernard's definition is this:—A substance taken in the external medium "necessary for the maintenance of the phenomena of the healthy organism and for the reparation of the losses it constantly suffers." "A substance which supplies an element necessary for the constitution of the organism, or which diminishes its disintegration" (stored-up food); this is the definition of C. Voit, the German physiologist. M. Duclaux says, in his turn, but in far too general terms, that it is a substance which contributes to assure the sound functional activity of any of the organs of the living being. None of these ways of describing food gives a complete idea.

Food, the Source of Energy and Matter.—The inter