O, the empirical formula of fat. Or the starch may be changed, by vital chemistry, into four equivalents of carbonic acid (C, O), four equivalents of olefiant gas (C3, H3), and two equivalents of water (H, O2). Or if we admit that the nitrogen of the atmosphere combines, in the digestive process, with the elements of food, —of which there can be little doubt (185), then four equivalents of starch, may be converted into one equivalent of protein (C1, H, N°, O11), and four of water, with a separation of oxygen. Thus, under a full vegetable diet (in which starch abounds), a sedentary lifeespecially if the pores of the skin are not kept open by frequent ablutions-will generally conduce to the formation of fat; but if abundant oxygen and nitrogen be supplied by exercise, a less amount of oxygen is then requisite from the food; and the chyle-which might, in other circumstances, have produced fat-may now be converted into fibrin, to supply the waste of tissue arising from muscular exertion. 201. Here then is manifest a ray of that divine wis dom, which shines so gloriously in every department of nature, when carefully investigated. We need no longer regard the nitrogen, which constitutes four-fifths of the atmosphere, as an inert and useless gas; but, like oxygen, as an important and essential aliment for the support of animal life. The two gases are held in a weak, and perhaps only mechanical combination, in order that each may, in its turn, as circumstances require, subserve the interests of vitality. If animals were so constituted as to render necessary a precise amount of any element in the food to which their instincts direct them, and if their organs were so limited in their functious as to be incapable of fulfilling any other duty but that for which they were specially intended, then would life be subject to continual interruption; and disease and death would spread ruin and devastation in every direction. Neither men nor the lower animals are at all times so situated, as to be able to procure, in sufficient abundance, that food which contains all the elements in the precise proportion and mode of combination best suited to their organization: the atmosphere, therefore, presents an immense reservoir, always at hand to make up deficiencies, by means of mastication or respiration; and the digestive, chylopoietic, and secerning organs, are endowed with such capabilities as to vary, within certain bounds, their proper functions; and to seize, with unerring precision, those elements of the atmospheric air, of which the ingesta and circulating fluids are deficient. 202. In applying these views to man, on a natural or vegetable diet, the following suggestions are offered. In warm climates, where an elevated temperature is incompatible with great muscular exertion, nature has provided a bountiful and pleasant repast of fruit, rice, and other vegetables possessing a considerable proportion of carbon and hydrogen, but little nitrogen. By virtue of affinities modified by vital agency, these nutritive substances are formed (in the stomach, duodenum, &c.) into new compounds, by a rearrangement of their elements, and by a combination with those of the atmosphere; thus producing either protein or fat, as the wants of the system may determine. If the tissues are wasted by exercise, more oxygen and nitrogen are supplied by the atmosphere, so as to prevent the formation of oleaginous compounds; and the albuminous principles that result, are converted into fibrin to renovate the system: but if sedentary occupations preponderate, less fibrin becomes necessary; the deficient supply of air causes more oxygen to be separated from the food; and an increase of fat is the consequence, -especially if the food be in excess. If a more azotized diet be indulged in, then-as there is less occasion for the formation of protein from the starch-the carbonaceous compounds must be eliminated by the skin, liver, and lungs; but, as the cutaneous surface, especially of the white variety of mankind, is not constituted for performing the additional duty now demanded of it, and as in these circumstances there is a deficient supply of oxygen to the lungs, carbon accumulates in the blood; and the liver is called into an excessive exercise of its function, in consequence of the inactivity of the skin and lungs. Hence the prevalence of hepatic diseases in hot climates. 203. In cold and temperate regions, wheat and other azotized products may be more freely indulged in; and the carbonaceous principles of food are then left at liberty for the respiratory function; muscular exercise becomes more easy and pleasant, and caloric is more abundantly formed. The inhabitants of these countries are more exposed to diseases of the chest, and that numerous train of distressing complaints arising from the presence of an abnormal proportion of lithic acid in the system, such as gout, rheumatism, gravel, &c. The extreme indulgence in animal food, in these countries, becomes the predisposing cause of all these diseases, as well as of dyspepsia and liver-complaints (313). If flesh, or other highly azotized food, be taken with a very small proportion of starchy matter, the sufferings of the dyspeptic are alleviated, as every medical practitioner is aware; because there is then less carbon for the liver to separate; but this diet demands more exercise from the lungs, in consequence of the diminished supply of oxygen from the food; hence its danger to persons who are threatened with phthisis (254, 362, and 463); as well as to gouty individuals,—from its favouring the production of lithic acid (316). If the dyspeptic were entirely to abandon the use of animal food, and adopt a diet of fruit and farinacea, not only would the disease be palliated, (as by the above treatment,) but, in the generality of cases, entirely cured, without throwing an additional burden upon either the lungs or kidneys;-the former having their labour remitted by the disengagement of oxygen from the food, during the conversion of starch into protein; and the latter having less duty to perform, in consequence of the diminished supply of substances containing protein ready formed. There is therefore no real contradiction in stating, that while a diet of lean animal food and bread, or a very sparing supply of vegetables, greatly relieves the dyspeptic; an exclusively vegetable diet is still more efficacious (357). Under the former, no greater quantity of the non-azotized principles is received, than is necessary for the supply of the respiratory process, and for the production of animal heat;-the flesh yielding the requisite amount of albumen for the repair of the fabric. If the proportion of vegetable food be considerably increased, the nutrient matter will be in excess; and, consequently, the blood may become surcharged with carbon, or nitrogenized principles; the former stimulating the liver, the latter the kidneys. Under the exclusively vegetable diet, the non-azotized principles unite with the nitrogen of the atmosphere, to supply the protein which is deficient in the food; thus preventing too great an accumulation of carbon but in proportion as animal food is superadded, this conversion becomes unnecessary, and the surplus must be disposed of by other means;-being transmuted either into fat, or non-vitalized albumen; and thereby giving rise to hepatic complaints, scrofula, tubercles, gout, and other diseases. 204. Some have contended, that a mixture of animal and vegetable food, in certain proportions, contains, within the least possible weight, all the chemical principles requisite for supplying the waste of structure, and for the production of animal heat; and that neither animal nor vegetable food, taken separately, answers the purpose so well, unless in much larger quantities. Presuming that a man, taking moderate exercise, requires 18 ozs. of starch, and 5 ozs. of albumen or gluten, &c., in twenty-four hours, Mr. Johnston calculates, that these will be best supplied by 12tb. of bread and half a pound of animal food. Thus : * *JAMES T. W. JOHNSTON'S ELEMENTS OF AGRICULTURAL CHEMISTRY AND GEOLOGY. |