The physiology of digestion, considered with relation to the principles of dietetics / by Andrew Combe.

  • Combe, Andrew, 1797-1847.
Date:
1860
Catalogue details

Licence: Public Domain Mark

Credit: The physiology of digestion, considered with relation to the principles of dietetics / by Andrew Combe. Source: Wellcome Collection.

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    is excessive, are accordingly almost coustantly under tlie influence of thirst; whereas those wlio are employed in professions requiring only moderate exertion in a temperate atmosphere, and in whom the fluid secretions are very moderate, rarely experience the sensation in an urgent degree. For the same reason, great loss of blood induces excessive and intolerahle thirst; and the generous self-denial of him who, in the battle-field, passed the cup to his wounded neighbour without stop- ping even to moisten his own lips, can be fully appreciated only by those who have themselves experienced the urgency of thirst in similar circum- stances. Thirst varies in intensity also ac- cording to the nature of the food. If the diet be of a hot and stimulating qua- lity, such as results from a free admix- ture of spices, the desire for liquids is greatly increased. The same thing happens if the food be dry and solid. The purpose of the increased thirst in the former circumstances is manifestly to dilute and diminish the irritation of the stimulant, and thereby prevent the injury which it would otherwise inflict. The same principle explains the thirst experienced by those who drink too much wine. In instances of this kind I have heard great thirst in the evening and during the night com- plained of as habitual, without the persons even suspecting that it was owing to the wine ; and yet, on ab- staining from the latter, their thirst very soon disappeared. Thirst is pro- duced by dry food, because a certain amount of liquid being necessary for digestion, if this be not present in the food itself, it is withdrawn from the blood, in the mouth and stomach, by means of the saliva and gastric juice ; and hence, the necessity of replacing this fluid gives rise to tlie sensation of thirst. Salt food produces thirst in a twofold way; first, by its stimulating properties, whereby the exhalations of the s\un are increased; and, secondbj, by the power which a saline solution has of attracting the water of tlio blood, on the principle of exosmosis, as explained in Chapter VI. Continued thirst, it is well knovm, is much more intolerable than conti- nued hunger. The mass of circula- ting fluid in the body is very great, and, as the various excretions consist chiefly of fluid matter, it necessarily happens that when these have been eliminated for a considerable time without any liquid being received in- to tlie system, the proportion of solid matter in the body becomes unduly large. The blood, consequently, be- comes thicker and changed in quality, and much more irritating than in its natural state. The craving of thirst is thus generally rendered more urgent and overpowering than that of hunger. In Asiatic cholera, the watery por- tion of the blood, on which its fluidity depends, is drained off with great ra- pidity; and the result is, in the first place, an almost complete stoppage of the circulation, and, in the second, a constant craving for drink to supply the place of the lost serum, which con- sists chiefly of water holding some of the alkaline salts in solution. This circumstance explains, in some degree, the extraordinary effects which have been produced, even in the worst stages of the disease when life seemed almost extinct, by injecting large quantities of saline solutions into the veins. Pa- tients apparently on the verge of ex- istence, cold, pulseless, and inanimate, have, in the course of a few minutes, been enabled by this means to sit up in bed, and to exhibit, for the moment, all the signs of restored strength and health. The effect, however, was as evanescent as it was striking, and not one of the patients so treated ulti- mately recovered. Fluids taken into the stomach, it is proper to observe, are not subjected to the slow process of digestion, but are absorbed directly into the system; so that, when we take amoderatedraught, the whole of it is imbibed from the stomach in a very few minutes. Keep- ing in view this fact, and the above striking illustration of the influence of the condition of the blood upon the body at large, we can easily con- ceive why, in a state of exhaustion from abstinence, drink should be mora