147. As the introduction of solid aliment into the stomach is for the purpose of furnishing materials for the repair of the different textures of the body, so is a supply of liquid matter, essentially necessary to replace those various fluids which are constantly ejected from the body, during the exercise of its different functions. The necessity of this supply, as well as its quantity are both indicated by a certain feeling known by the name of thirst. In this point of view, therefore, drinks ought to be considered as real aliments; and, indeed, it is a question whether they may not also undergo certain decompositions in the body, and be made to surrender elements for the formation of solid parts'. The chyme and chyle may also require the assistance of some liquid medium to favour the absorption of its finer and more nutritive parts, which, by increasing the fluidity of the mass, will expedite the numerous combinations it is destined to undergo. In every point of view, therefore, dilution is an essential operation; and an animal will not only endure the sensation of hunger with more tranquillity than that of thirst, but he will survive longer under the privation of solid than of liquid aliment2. Unfortunately, however, those instincts which nature implanted in us for our guidance have been eradicated by the habits of artificial life: thirst is so rarely experienced, that the very sensation is associated with the idea of disease.

The consequence is, that we have been abandoned to the control of our caprice in the selection and use of these agents, - a circumstance which has given origin to numerous disorders. The quantity of diluents which each person may require will depend upon individual peculiarity, climate, nature of the solid aliment, etc.

1 Fish, especially the cetaceous tribe, decompose water, and live upon its hydrogen.

2 Redi (Osservaz. intorno agli Anim. viventi, etc. No. 34.) instituted a series of experiments, with the sole view of ascertaining how long animals can live without food. Of a number of capons which he kept without either solid or liquid aliment, not one survived the ninth day; hut one to which he allowed water, drank it with avidity, and did not perish until the twentieth day. See our work on Medical Jurisprudence, Art. "Death by Starvation," vol. ii. p. 67.

148. In appreciating the effects of liquids upon the human body, there are several circumstances independent of the quality of the fluid which deserve some notice; such as temperature, volume, and the period of potation. Although fluids of the usual temperature of the air are grateful and congenial to a healthy stomach, persons disposed to dyspepsia frequently require them to be raised to the temperature of the body; for the stomach, not having sufficient vital energy to establish the re-action which the sudden impression of cold produces in a healthy condition, falls into a state of collapse, and is consequently unable to proceed in the performance of its requisite duties 1 It deserves notice, however, that fluids heated much above the temperature of the body are equally injurious: it is true that they will frequently, from their stimulus, afford present relief; but it will always be at the expense of future suffering, and be compensated by subsequent debility. Iced fluids should not be taken, under any circumstances, by those who have delicate stomachs, especially after a meal, the digestion of which is thus retarded, or wholly prevented.

1 This remark applies particularly to the residents of hot climates, whose stomachs are always more or less enfeebled. It appears that the Romans were in the habit of drinking tepid potations at their meals. See Juvenal, Sat. V., v. 63.

149. It is a popular idea that hot liquids injure the teeth. I entertain great doubts upon the subject. Ribe, in a paper published in the Amcenitates Academicce, observes, that "Man is the only animal accustomed to hot food, and almost the only one affected with carious teeth." This is far from being true; the term of life in all the graminivorous classes appears to be principally limited by the decay of the teeth, and forms an insuperable obstacle to the prolongation of their existence much beyond the term when they have attained to the perfection of their kind1.

150. The quantity or volume of liquid taken at once into the stomach is a circumstance of material consequence. The reader must refer to that part of the work in which the digestion of drinks is explained (97), in order to understand the importance of the considerations which this question embraces. It is evident that if the stomach be distended with fluid, the digestion of its solid contents must meet with considerable impediment; its bulk will stimulate the muscular fibres to contract too rapidly, and thus to expel the food before it has undergone the necessary changes; while, at the same time, it is said that the gastric juice becomes too dilute to fulfil the objects of its secretion. Upon this latter point I entertain some doubt: the secretions of the stomach are not very soluble in water; and it has been already stated with what extreme difficulty the coagulating quality of the gastric membrane is removed by washing. Be this, however, as it may, it is evident, that if the solid matter be diffused through a large quantity of liquid, it cannot be so easily acted upon by the gastric juice; nor can it be converted into that pultaceous mass which appears to be a preliminary step to its digestion.

On the other hand, if the food be too hard or dry, its necessary change by the churning of the stomach cannot be accomplished, and the progress of digestion will be impeded. It therefore follows, that different aliments will require different quantities of liquid to assist their chymification. Animal food demands, of course, a greater quantity of drink than vegetable food; roasted, than boiled meat; and baked still more than roasted. The next question to be considered is, as to the most suitable period for taking liquids; and this is, in some measure, answered by the preceding observations. By drinking before a meal, we place the stomach in a very unfit condition for the duties it has to perform. By drinking during a meal, we shall assist digestion, if the solid matter be of a nature to require it; and impede it, if the quantity taken renders the mass too liquid. Those physicians, therefore, who have insisted upon the necessity of a total abstinence of liquid during a meal, appear to have forgotten that every general rule must be regulated by circumstances. The best test of its necessity is afforded by the sensations of the individual, which ought not to be disregarded merely because they appear in opposition to some preconceived theory.

The valetudinarian who, without the feeling of thirst, drinks during a meal because he has heard that it assists digestion; and he who abstains from liquid, in opposition to this feeling, in consequence of the clamour which the partizans of a popular lecturer have raised against the custom, will equally err, and contribute to the increase of the evil they so anxiously seek to obviate. Dr. W. Philip has stated a fact, the truth of which my own experience justifies, that "eating too fast causes thirst: for the food being swallowed without a due admixture of saliva, the mass formed in the stomach is too dry." The same habit is also a common cause of costiveness. I may conclude these remarks by observing, that as hunger and thirst are, to a certain extent, incompatible sensations, it is probable nature intended that the appetite for food should first be satisfied, before a supply of drink becomes necessary; and if our food possess that degree of succulence which characterizes digestible aliment, there will seldom be any occasion for it.

But, under any circumstances, the quantity taken should be small: it is during the intervals of our solid meals that the liquid necessary for the repair of our fluids should be taken; and both theory and experience appear in this respect to conform, and to demonstrate the advantage which attends a liquid repast about four or five hours after the solid meal. At about this period the chyle has entered its proper vessels, and is flowing into the blood, in order to undergo its final changes. Then it is that the stomach, having disposed of its charge receives the wholesome draught with the greatest advantage: then it is that the blood, impregnated with new materials, requires the assistance of a diluent to complete their sanguification, and to carry off the superfluous matter; and it is then that the kidneys and the skin will require the aid of additional water, to assist the performance of their functions. The common beverage of tea, or some analogous repast, originally suggested no doubt by an instinctive desire for liquid at this period, is thus sanctioned by theory, while its advantages are established by experience.

So, again, after the repose of the night, we feel an instinctive desire for liquids, as already stated (136) in consequence of the loss of fluids sustained by the body during sleep.

1 In the elephant, who rivals, or perhaps exceeds, man in duration of life, a peculiar provision is found to exist for the purpose of renewing the teeth. The grinding teeth, or molares, of the elephant, which consist each of a single piece of bone, intermingled with enamel, are so constructed as to continue growing from behind, in proportion as they are worn away in front by the process of mastication; so that their duration is coeval with that of the animal.