TWO CAUSES OF THIRST. 37 three-and-twenty out of the hundred and forty-six still breathed. These were subsequently revived. Although the principal cause of this mortality must be ascribed to the vitiated atmosphere rather than to Thirst, we nevertheless see some of the frightful phenomena of Thirst exemplified in this narrative. Death by asphyxia (from vitiated air) is generally peaceful, and not at all such as is described in the foregoing. Attention is moreover called to certain passages in italics. These show that the sensation of Thirst is not merely a sensation dependent on a deficiency of liquid in the system, but a local sensation dependent on a local disturbance the more water these men drank, the more dreadful seemed their thirst; and the mere sight of water rendered the sensation, which before was endurable, quite intolerable. The increase of the sensation following a supply of water, would be wholly inexplicable to those who maintain that the proximate cause of Thirst is deficiency of liquid; but it is not wholly inexplicable, if we regard the deficiency as the primary, not the proximate cause; for this primary cause having set up a feverish condition in the mouth and throat, that condition would continue after the original cause had cease to exist. The stimulus of cold water is only a momentary relief in this case, and exaggerates the sensation by stimulating a greater flow of blood to the parts. If, instead of cold water, a little lukewarm tea, or milk-and-water, had been drunk, permanent relief would have been attained; or if, instead of cold water, a lump of ice had been taken into the mouth, and allowed to melt there, the effect would have been very different-a transitory application of cold increasing the flow of blood, a continuous application driving it away. If, therefore, the reader is ever suffering from intense thirst, let him remember that tepid drinks are better than cold drinks, ice is better than water. We must not, however, forget that although, where a de ficiency of liquid has occasioned a feverish condition of the mouth and throat, no supply of cold liquid will at once remove that condition, the relief of the Systemic sensation not immediately producing relief of the local sensation, nevertheless, so long as the system is in need of liquid, the feeling of thirst must continue. Claude Bernard observed that a dog which had an opening in its stomach drank unceasingly, because the water ran out as fast as it was swallowed; in vain the water moistened mouth and throat on its way to the stomach, Thirst was not appeased because the water was not absorbed. The dog drank till fatigue forced it to pause, and a few minutes afterwards recommenced the same hopeless toil; but no sooner was the opening closed, and the water retained in the stomach, from whence it was absorbed into the system, than thirst quickly vanished.* After learning the physiological importance of water, and remembering how the water is continually being removed from the body in respiration, perspiration, and the various excretions, we are greatly puzzled by the great variations which animals exhibit in the quantity they drink. The difficulty is not explained by a reference to the food of the animals, for some vegetable feeders require large quantities of water, while others subsist for months without drinking, the supply they receive in the vegetables they eat being sufficient for their wants. Dr. Livingstone found the elands on the Kalahari Desert, although in places where water was perfectly inaccessible, with every indication of being in splendid condition, and their stomachs actually contained considerable quantities of water. "I examined carefully the whole alimentary canal," he says, "in order to see if there were any peculiarity which might account for the fact that these ani * CLAUDE BERNARD: Leçons de Physiologie Expérimentale, ii. 51. THE DRINK OF ANIMALS. 39 mals can subsist for months together without drinking, but found nothing. Other animals, such as the düiker (Cephalopus mergens), the steinbuck (Tragulus rupestris), the gemsbuck (Oryx capensis), and the porcupine, are all able to subsist for many months at a time by living on bulbs and tubers containing moisture. Some animals, on the other hand, are never seen but in the vicinity of water. The pres ence of the rhinoceros, buffalo, and gnu, of the giraffe, zebra, and pallah (Antelope melampus), is always a certain indication of water being within seven or eight miles."* The only solution of the difficulty which presents itself to my mind is, that animals which can subsist long without drinking, do not lose more water by evaporation and excretion than can be replaced by their vegetable food, since that they require the same amount of water as other animals for the performance of all their functions is physiologically certain. It has been observed that, in persons who voluntarily abstain from drinking, the excretions were diminished to a minimum. Sauvages, in his Nosologia Medica, mentions the case of a member of the University of Toulouse who never knew what thirst was, and passed several months, even in the heat of summer, without drinking. Another case is cited by the same author of a woman who took no liquid for forty days. M. Bérard thinks that the marvellousness of these facts disappears when we remember how much liquid is contained in all food;† but I am rather disposed to doubt the accuracy of the facts than to accept such an explanation: at any rate, they are facts so very exceptional as to have little bearing on our general argument. The effects of Thirst are first a dryness of the mouth, palate, and throat; the secretions become less copious; the mouth is covered with a thick mucus, the tongue cleaves to * LIVINGSTONE: Missionary Travels in South Africa, p. 56. the palate, the voice becomes hoarse. Then the eyes flash fire, the breathing becomes difficult, a feverish excitement, often passing into delirium, comes on.* Sleep is fitful, and distressed by dreams akin to the torments of Tantalus. The men shipwrecked in the " Medusa" dreamt constantly of shady woods and running streams. It is to be noticed that the sensation of Thirst is never agreeable, no matter how slight it may be, and in this respect is unlike Hunger, which, in its incipient state of Appetite, is decidedly agreeable. The bodies of those who have perished from Thirst show a general dryness of all the tissues, a thickening of the humours, a certain degree of coagulation of the blood, numberless indications of inflammation, and sometimes gangrene of the principal viscera. According to Longet, Thirst kills by an inflammatory fever, Hunger by a putrid fever.t Such are Hunger and Thirst, two mighty impulses, beneficent and terrible, monitors ever vigilant, warning us of the need there is for Food and Drink-sources of exquisite pleas ure and of exquisite pains, motives to strenuous endeavour, and servants to our higher aims. We are all familiar with them in their gentler aspects; may we never know them in their dreadful importunities! *From some experiments by Professor E. HARLESS, in Munich, at which I assisted, it appeared that the nerves gain an extraordinary increase in their excitability as their proportion of water decreases. (For a fuller account of this remarkable fact, see BIRKNER, Das Wasser der Nerven, 1858.) The nervous excitability delirium, and sleeplessness, occasioned by Thirst, may be greatly owing to this cause. + LONGET: Traité de Physiologie. CHAPTER II. FOOD AND DRINK. SECTION I-ON THE NATURE OF FOOD. Varieties of food-The eaters of clay-The chemical and physiological methods of investigation-"One man's meat another man's poison," illustrated-A caution to parents-Wholesome and unwholesome food-Relation of food to the organism-Vital process incapable of chemical explanation-Difference between chemistry and physiology-A canon of philosophy-Is the family a type of the State?-Chemical problems are quantitative; physiological problems qualitative-Liebig's classification of food into plastic and respiratory not acceptable-Liebig's error arises from his taking the chemical point of view-Facts against him-Experiments on animals-The rice-eating Hindoos-The food in cold countries-Results of inquiry-Inorganic food-Nutrition in plants and animals misunderstood-Phosphate of lime in the body; amount of water in the body; amount of salt-uses of salt-The law of endosmosis. An Irish peasant, in a windowless hut, dining off a meal of potatoes and skimmed milk, flavoured by the aroma of a lively imagination as each mouthful is "pointed" at the side of bacon hanging against the wall, and a London Alderman seated at a Guildhall feast, are two figures presenting an impressive contrast of the varieties of food with which, in the restless activity of life, the human organism repairs its incessant waste. Potatoes and skimmed milk, and it may be a little sea-weed, supply the wants of the one; before the other there is spread a wasteful profusion of turtle captured on the North American coasts, of turkey reared in quiet |