In proof of the sensation of thirst being greatly dependent upon the quantity of fluid circulating in the vessels, Professor Dunglison of Maryland refers to the fact, mentioned by Dupuytren, that he “succeeded in allaying the thirst of animals by injecting milk, whey, water, and other fluids into their veins;” and to Orfila’s statement, “that, in his toxicological experiments, he frequently allayed, in this way, the excessive thirst of animals to which he had administered poison, and which were incapable of drinking, owing to the œsophagus having been tied. He found, also, that the blood of animals was more and more deprived of its watery portions as the abstinence from liquids was more prolonged;”[59] and hence the greater thirst naturally experienced under such circumstances.
As a general rule, then, the desire for liquids will in itself be an indication of their propriety; but in gratifying it, we should be careful not to drink so fast as either to distend the stomach beyond proper bounds, or to disturb the progress of digestion by undue dilution too soon after eating. Many persons, from habit rather than thirst, impair the tone of the stomach by drinking largely during or immediately after meals, and thus relaxing the mucous coat, and probably affecting the quality of its secretions. If the gastric juice be greatly diluted by extraneous fluids, it is natural to suppose that its solvent power must be diminished; but whether this explanation be sound or not, the practice of drinking frequently is certainly hurtful, and therefore we ought to avoid it.
Experience proves that a moderate quantity of liquid during a meal is beneficial; and if we drink little at a time, the risk of exceeding the proper limit will be very small. Dyspeptics, however, ought to be on their guard against taking too much, as they are apt to be misled by uneasy sensations in the region of the stomach, which are relieved for the moment, but afterwards aggravated, by the free dilution of the food. Those, also, who live well, and are in the habit of taking wine daily whether the system requires it or not, often fall into the error of excessive indulgence in liquids to mitigate the thirst and irritability which the unnecessary use of stimulus never fails to induce, especially at night. The continual dilution, however, adds to the mischief, by increasing the debility of the stomach, and, as pointed out in the chapter on Thirst, the only effectual remedy is to adapt the diet and regimen to the real wants of the constitution. Except in disease, a continually recurring thirst must proceed from mismanagement, and it is to be satisfied by an improved and rational regimen, and not by oceans of fluid, which only weaken the stomach still more, and aggravate the craving they are meant to cure.
The opinion is very prevalent, that mild drinks may be taken with most advantage about three or four hours after a solid meal; and, certainly, the almost universal use of tea or coffee about that time appears to sanction its soundness. Theoretically, too, we might expect this result; for digestion is then nearly over, and any food remaining in the stomach is already in a fluid state. Many objections, however, have been made to both tea and coffee as an evening beverage, but most of them seem to me to apply to their undue quantity and strength rather than to their temperate use. When made very strong, or taken in large quantity, especially late in the evening, they not only ruin the stomach, but very seriously derange the health of the brain and nervous system.
The question of drink is of little importance as regards breakfast. During the night, the chief expenditure of the system—by perspiration, urine, and exhalation from the lungs—is of a fluid nature, and hence there is a marked and general preference of fluids as part of our first meal. In this country, accordingly, tea, coffee, and chocolate, are in almost universal use for breakfast, and no other liquid is required merely as drink. If, from the mode of life or other causes, thirst be excited in the forenoon, no valid objection can be urged against its moderate and reasonable gratification.
The temperature at which liquids are taken is a matter of perhaps greater consequence than it is usually considered. As regards the teeth, we have already seen that either very cold or very hot substances coming into contact with them are apt to be injurious. As regards the stomach, the same principle holds true; and when we consider the multitude and intricacy of its nervous connexions with other vital organs, we can scarcely be surprised at even sudden death being frequently caused by drinking ice-cold water when the body is weakened by profuse perspiration. Of the various subjects connected with digestion on which Dr Beaumont has thrown light by his experiments on St Martin, this is one of the few which he has omitted to investigate with his usual diligence and accuracy; a circumstance which is the more remarkable, because an incidental observation of his own seems, from its singularity, to have been well calculated to direct his attention to its consideration. On the occasion alluded to, when a gill of water, at the temperature of 55° Fahr., was received into the empty stomach, in which the thermometer previously indicated a heat of 99°, Dr Beaumont remarked that it immediately diffused itself over the interior surface, and brought down the temperature to 70°, at which it stood for a few minutes, and then began again to rise very slowly. It was not till thirty minutes had elapsed, and all the water been for some time absorbed, that the mercury regained its former level of 99°. This is an important fact, and it is curious that Dr Beaumont did not think of following it up by a regular series of experiments, to ascertain the effects of cold and hot drinks on the progress of digestion and on the general system. It is well known, for example, that a copious draught of cold water, taken in a state of perspiration and fatigue, is often instantly fatal; but its operation has never been satisfactorily explained. The above experiment, however, throws some light on it; for if a single gill of water at 55° (which is not by any means a low temperature) is able to reduce the heat of the stomach in a moment by no less than twenty-nine degrees, when neither fatigue nor perspiration is present to add to its effect, the influence of a large quantity, such as is usually drunk by harvest-labourers and others who die of it, and at a still lower temperature, must undoubtedly be much more powerful and permanent, especially when the bodily energies and means of resisting the shock are impaired by previous labour and exhaustion under a burning sun. In these cases the shock necessarily arising from such a sudden and extensive fall of temperature is greatly increased by the position of the stomach in the very centre of the vital organs, to all of which it is most intimately linked by the numerous nervous connexions given for the express purpose of extending the range and direction of its sympathies.
Keeping in mind the great depression of temperature caused by swallowing so small a quantity of cold water, and also the ascertained fact that a heat of about 100° is requisite for healthy digestion, we shall have no difficulty in accounting for the frequent injurious consequences arising from considerable quantities of ice-cream being hastily eaten, as they often are, at the end of a substantial dinner. The immediate effects of the rapid abstraction of heat to which they give rise in the stomach, are the instantaneous contraction and diminished action of its bloodvessels, the consequent stoppage of the gastric secretion, diminished sensibility of its nerves and muscular fibres, and, lastly, disturbance of the heart and neighbouring vital organs, both by sympathy and by the direct abstraction of their heat. Such, at least, are the consequences which flow from the application of cold to parts exposed to observation, and partially verified by Dr Beaumont in the case of the stomach; and if the analogy holds throughout, as there is every reason to believe, we cannot wonder that the free use of ice-cream at the end of a good dinner or supper should retard and even arrest digestion in a person delicately constituted.
In thus condemning the free use of ices at the end of a substantial meal, I do not, however, mean to say that a few tea-spoonfuls of them, eaten slowly, and allowed to acquire a higher temperature before reaching the stomach, will do permanent injury to a person in health and in the enjoyment of sound digestion. Many eat them in this way and are little the worse; partly from the subsequent reaction, as in bathing, being sufficient to counteract the depressing influence, and partly from a person in vigorous health being able to throw off causes of disease from which those who are less robustly constituted suffer severely. My belief however is, that the tendency of ices, taken in such circumstances, is to produce mischief. A healthy person, for example, may possess vigour enough to escape injury from immersion in cold water, caused by the ice giving way when skating; but as well might it be inferred, on that account, that a similar immersion would be generally innocuous, and even salubrious, as that all may safely eat ices freely because a given individual has done so with impunity. Dr Beaumont’s experiment with the cold water shews clearly that the effect is to lower the vital tone of the stomach; and, such being the case, those whose digestion is weak ought to be careful against impairing it still farther by the use of ices. In some instances, however, it is not improbable that they help to neutralize the bad effects of hot soup, and other dishes eaten at too high a temperature.
The use of cold or iced water in hot weather and in warm climates, when digestion is not going on and exhaustion is not present, is so far from being necessarily hurtful, that with proper caution it may prove both grateful and refreshing. In Italy, accordingly, ice is considered so much a necessary of life in summer, that in Naples and other places the confectioners are punished by a fine if they allow their supply to fall short. In Virginia, too, where, we are told by Professor Dunglison, it was very common some years ago for the labourers in the harvest-field to be killed by drinking copiously of spring-water while overheated, cases of death have become extremely unfrequent since the custom was introduced of supplying them with ice. When water was taken, it was always hastily and in large quantity, so that the immediate effect on the system was greater than could possibly arise from the small quantity of ice which is required for quenching thirst. The very slowness, indeed, with which ice melts, not only prevents much being taken, but causes the water procured from it to reach a higher and safer temperature before it arrives at the stomach.[60] Hence, when ices are taken, the more slowly they are eaten the more refreshing and salubrious will they become, because the less violent will be their action upon the nerves, bloodvessels, and membranes of the stomach. From the close sympathy existing between the stomach, and the skin, a single tea-spoonful of ice-cream suddenly swallowed when the body is weak and perspiring, will produce as instantaneous a sense of chill as a pail of cold water dashed over the surface; and on account of this very power over the vital actions of the stomach, ice has of late been cautiously and beneficially prescribed to subdue inflammation of that organ.
Liquids, such as soup, tea, and coffee, taken at a very high temperature, are also injurious, but not in the same degree. They relax the mucous membrane and weaken the action of the muscular coat, and in so far tend to impair digestion. The fittest temperature for both solid and liquid food is perhaps about the natural heat of the body, or a little above 100°. Dr Dunglison, however, and some other physiologists, regard hot fluids as stimulating to the stomach, and therefore conducive to digestion; but he admits that debility is their ultimate effect.