The physiology of digestion, considered with relation to the principles of dietetics / [Andrew Combe] ; edited, and adapted to the present state of physiological and chemical science, by James Coxe.

  • Combe, Andrew, 1797-1847
Date:
1849
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Licence: Public Domain Mark

Credit: The physiology of digestion, considered with relation to the principles of dietetics / [Andrew Combe] ; edited, and adapted to the present state of physiological and chemical science, by James Coxe. Source: Wellcome Collection.

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    speedily restorative and refreshing than food. Thirst is intended to direct us when and in what quantity we ought to drink ; and so long as we lead a life of ordinary health and activity, and confine ourselves to the fluids with which nature provides us, there is little chance of our going far wrong by lis- tening toitscalls. Butwhen webecome indolent and dyspeptic, or resort to liquors, which excite a thirst not re- cognised by Nature, the principle ceases to apply. At present, however, my observations refer only to simple drinks, such as water, and to the state of health ; and Ishall touch upon other liquids when treating of diet, in a sub- sequent part of the volume. Many persons, without experiencing any real thirst, habitually indulge in potations of water or beer at all hours of the day, and to an extraordinary extent, and feel unhappy when suddenly re- stricted in the indulgence. But this temporary discomfort ought not to be considered as indicating that these po- tations are really necessary ; because the same result happens in the analo- gous instances of smoking or snuffing. All three are abuses and perversions of nature; and the uneasiness attend- ing the sudden cessation of the beer or water drinking is no more a proof of either fluid being required, than that consequent on giving up cigar- smoking is an indication that Nature designed the lungs for the reception of the impure effluvia of the tobacco leaf instead of the fresh breezes of hea- ven. CHAPTER III. GENERAL QUALITIES OF FOOD. Chemical composition of the animal body—Its ma- terials undergo a constant expenditure during every yital action, and in the lungs—Food must therefore contain the substances necessary for the repair of this expenditure—and must be soluble in the gastric juice—Division of food into nitrogenous and non-nitrogenous; the former supplying materials for restoring to the tissues what they have lost during vital action, and the latter furnishing materials for respiration—Ni- trogenous artielos of food comprise what are called protein compounds, namely fibrin, albu- men, and casein—Composition of these—Non- nitrogenous aliments are needed only for the support of animal heat—Manner in which this end is accomplished—This class of aliments com- prises the hydrates of carbon, namely starch, sugar, gum, &¢.—All substances necessary for nutrition are contained in milk—Dr Prout’s con- sequent division of food into albuminous, sac- charine, and oily—Digestion defined, HAVING seen that the necdful sup- ply of nourishment is regularly de- manded by the appetite, we shall now direct the reader’s attention to a few of the general qualities of food, pre- vious to entering upon the description of the organs of digestion ; reserving till a later period the remarks we shall offer on the individual articles of diet. Food, in order to be nourishing, must contain a large amount of di- gestible organic compounds, a smaller proportion of inorganic salts, and a certain quantity of water. The ani- mal body contains nitrogen, carbon, oxygen, and hydrogen, in great abun- dance, along with small quantities of chlorine, sulphur, phosphorus, potash, soda, lime, magnesia, and iron, and occasionally also minute proportions of silica, fluor, manganese, and copper. All vital action is accompanied by a certain expenditure of these substan- ees, which are accordingly found in the excretions of the body. Thelungs give off a large proportion of the car- bon and hydrogen ; the kidneys almost the whole of the nitrogen, together with a large proportion of the inor- ganic salts; while the alvine evacua- tions contain a mixture of carbon, ni- trogen, and inorganic matter. To be permanently nutritious, therefore, the food must yield such an amount of car- bon, nitrogen, water (oxide of hydrogen), and inorganic salts, as is necessary to rée- pair the waste of the body. If this con- dition be not fulfilled, the excretions will carry off more matter than is sup- plied to the system, and nutrition must of necessity be impaired. An essential requisite of all aliment is capability of solution in the gastric or stomach juice. No substance can afford nourishment without entering the blood, whichis the medium through which the nutritious particles are dis- tributed to every part of the body; and none can be taken up by the absorbents