Page:Life in Motion.djvu/161

Rh so-called proximate principles must exist in any dietary that can keep an animal healthy and strong. The reason of this is, that if you examine chemically almost any of the tissues of the animal, you find that they are built up of the same kind of proximate constituents. Suppose a chemist analysed muscle, he would find in it proteid matters in the form of a substance called myosin, along with other albuminous bodies; carbo-hydrates would be represented by glycogen, a kind of animal starch, and by sugar; fats are there also; and if he burnt the muscle, an ash would be left containing the same salts as we found in milk. But the constituents in the food stuffs are not quite the same as those in muscle, and they are therefore subjected to many chemical processes in digestion by which they are first converted into stuffs that exist in the blood. From these stuffs in the blood the muscle builds up its- substance. Now all of these stuffs, from the scientific point of view, contain energy in what is spoken of as a potential state, that is to say, it is resting, ready to be set free, ready to do work, and when it is set free it may become, as it does