VI.
In determining the nutritive value of aliments by the study of their chemical composition, we cannot adhere strictly to the results furnished by analysis. For, says Baron Liebig, we cannot reckon upon results in the human stomach with the same regularity as we would in the alembics of our laboratories.
Physiologists divide alimentary substances into two classes: the nitrogenous, which, according to Dumas, supply the demands of assimilation, and the non-nitrogenous, which are called by Liebig respiratories, from furnishing the products consumed by respiration. Neither the one nor the other will alone support life indefinitely, and when one or the other decreases below well-defined limits, health declines, and finally life becomes extinct from inanition.
Milne Edwards gives, as the mean amount of these two classes, required for all climates, not less than three hundred and fifteen grains of nitrogen and thirty-three hundred and fifty grains of carbon in the twenty-four hours. These views are adopted by most physiologists; yet the analyses of Schlossberger and Kemp indicate that the idea of estimating the value of food by the quantity of nitrogen it contains is a fallacious one.
The beautiful experiments of Bernard and the modern physiologists have unfolded many of the laws that regulate digestion and assimilation. Yet the human researches in the great arcana of nature are extremely limited, in comparison with the vast range of physical phenomena, and every day we are reminded of the remarks of Boerhaave to his students: “Let all these heroes of science meet together; let them take bread and wine, the food which forms the blood of man, and by assimilation contributes to the growth of the body; let them try by all their art, and assuredly they will not be able from these materials to produce a single drop of blood,—so much is the most common act of nature beyond the utmost efforts of the most extended science.”
The composition of the typical food of nature is revealed to us in the analysis of human milk.
VII.
The need of varied food is apparent to the casual observer, and it is well proven in the immortal work of Cabanis. “The experience of civilized life has shown,” says Professor Horsford, in his admirable pamphlet on the marching ration of armies, “that the human organism requires, to maintain it in health, both organic and inorganic food.
“Of the organic, it needs nitrogenous food for the support of the vital tissues for work; and saccharine, or oleaginous food, for warmth. Of the inorganic, it needs phosphates for the bones, brain, muscles, and blood; and salt for its influence on the circulation and the secretions, and for various purposes where soda is required for a base; and doubtless both phosphates and salt for many offices as yet imperfectly understood. ‘A man may be starved by depriving him of phosphates and salt, just as effectively as by depriving him of albumen or oil.’ (Dalton’s Physiology.)
“The salts of potassa, magnesia, and iron, of manganese, silica, and fluorine, are always present, and perform services of greater or less obvious moment in the animal economy. These organic and inorganic substances are essential, but they are not all that are needed. Man, especially when compelled to exhausting labor, requires beverages and condiments. He wants coffee, or tea, or cocoa; or, in the absence of these, he may feel a craving for wine or spirits. He wants salt, pepper, and vinegar. To preserve a sound body, then, there are required organic and inorganic food, beverages, and condiments.”