Life is only earned on by virtue of the continuous changes and expenditures which create the corresponding alimentary wants A full grown man, in good active health, uses up each day, calculated in the fresh state, about 500 grms of his flesh or of other albuminous compounds which form his blood and his tissues.
He burns a part of his fats and furnishes by their combustion, and by that of sugars and starches, which foods put at his disposal or which his organs provide him with, a quantity of energy which, calculated in heat amounts in the adult to about 2,400 Calories in 24 hours. He loses, besides, some water every day, 1300-1350 cc by urine, 600-700 cc by the skin, 450 by the lungs. He exhales a quantity of carbonic acid 1 containing 610-690 grms of oxygen and 230-260 grms of carbon.
He throws off nearly 240-270 grms of this last element by the total amount of his excretions He loses by his fasces or by the urine 22-23 grms of diffeient mineral salts, more than half formed of sea-salt Daily nourishment should provide for all this expenditure.
Foods are therefore the solid, liquid or gaseous materials, suitable, when they are introduced into the system, for repairing the losses made by the organs and for assuring the exercise of their functions. The flesh of animals, their fat, the gluten and starch of cereals, ordinary sugar, water, salt, the oxygen of the air itself, are foods, because they have the property of maintaining our functions and preventing organic decay.
On the other hand, the flesh and eggs of certain fishes and reptiles, the albuminoid matters of some vegetables, and of many mushrooms, certain gums and the sugars which correspond to them, the salts of heavy metals, the nitrogen of the air, ozone, etc are not foods because, notwithstanding their analogy with the preceding substances, they are unsuitable for the maintenance of life or for the reconstitution of tissues.
In reality, whatever may be its composition and actual form, a principle is only alimentary if it can be placed, in traversing the digestive tube or in reaching our organs, in such a form that these can utilize it either as constructive material or as a means of action. On this point it is expedient to give at once some explanations.
Here are some particles of yeast, yeast of beer or mucor racemosus of the pellicle of the grape, sown, protected from the air, in some sweetened must, or even in a solution of cane sugar, to which is added a small quantity of phosphates of potash and ammonia, and traces of sulphate of magnesia and lime, these little organisms are nourished, they multiply, and from their action results, with emission of heat, a production of materials of new formation, complex materials serving to construct the cells which have been formed.
Placed in contact with sweetened liquor, the cell of beer yeast takes possession at once of all the nitrogen of the ammoniacal salts, the sulphur of the sulphates, the phosphorus of the phosphates placed at its disposal. All these salts have nearly disappeared right from the very beginning. From the sugar already existing in the nutritive liquor, it has borrowed its carbon as well as the oxygen which is necessary to it, for it lives in surroundings deprived of air.
From the mass of these elements (although we are not able in the present state of our knowledge to indicate the sequence of the intermediary processes). It has formed most complex substances these albuminoids, phosphorated proteids, the cellulose, glycogen, etc , which we find in the cells of new formation.
The nutrition of the yeast, far from being an act of simple intussusception or of chemical deposition in the living cells of matter pre-existing in the primitive liquid as when a crystal. The little organism has broken up the chemical substances offered to it, it has extracted from them the radicals, or the parts which are suitable to it, and has combined them in the form of substances which the vital action had caused to disappear, and from these materials thus formed. It has nourished itself to the point where it has used these food stuffs to reproduce new cells capable of recommencing the same work.
To nourish oneself, is then, in reality, to produce at the expense of the food, whatever it may be, a series of acts of dislocation, of simplification, and as a corollary and complement, of new associations, from which results the reproduction of specific constituent principles which the vital action had destroyed.