accomplislied by one arrangement, than two agents at work, of which one has only the function of moderating the other. Nitrogen, being more than three-fourths of the air, must surely have a direct and positive use. Experiment shows that the blood sometimes absorbs nitrogen, sometimes exhales it; why should it not enter into combination with the blood whenever an additional quantity of it is required? When nitrogen meets with hydrogen in a nascent state within an enclosed space, they unite and form ammonia; and, since hydrogen is developed, not only in the whole extent of the alimentary canal, but also in the capillaries (or fibrous small tubes)—where the disintegration of the worn-out tissues takes place—we have all the conditions necessary for this combination.
[The Author here goes further into the opinions of other physiologists which, directly or indirectly, support his opinion, that the nitrogen contained in the tissues of man and of the herbivora may he obtained from the atmosphere when deficient in the food.]
That azote in food is not indispensable may also be inferred from other facts. Adanson asserts that the nomadic Moors live chiefly on gum senegal. Hasselquist relates that 1,000 Abyssinians subsisted for two months on gum arabic alone. Those who gather gum from the trees in Arabia and Senegal live (for a time) almost entirely on it, and six ounces in 24 hours have proved sufficient for a man's support. Humboldt observed the Caraccas mule-drivers to prefer unprepared sugar to fresh animal food; and it is well known that negroes become fat and vigorous from chewing the sugar-cane. Yet gum and sugar have little or no azote.
Potatoes and rice also have very little azote; yet are not at all bad food. Maize is said to contain no gluten, and little (if any) ready-formed saccharine matter; yet animals fattened on it become firm in flesh. Horses fed on it are strong and hardy; so are the races of men who make it their ordinary food. Apparently then, the necessary azote must be got from the air.
But if the opposite be true, and azote in the food is necessary, we now know that azote is present in most parts of vegetables, particularly in the seeds, juices, and nascent parts; the membranes alone being destitute of it. And, in general, all nutritive substances contain both principles, the glutinous and the saccharine, though in varying proportions. Dr. Prout has shown that milk contains an albuminous substance (casein, or the cheesy element), oily matter (the butter), and no inconsiderable amount of sugar; thus including his three staminal principles. But it must be carefully kept in mind that all good food contains also a large quantity of innutritious matter, which is as requisite for healthy digestion as that which is nutritious.
The experiments of Liebig and other excellent chemists have
