Zoonomia; Or, the Laws of Organic Life, Vol. II

by Erasmus Darwin

SPECIES.

[1]. Sitis. Thirst. The senses of thirst and of hunger seem to have this connection, that the former is situated at the upper end, and the latter at the lower end of the same canal. One about the pharinx, where the œsophagus opens into the mouth, and the other about the cardia ventriculi, where it opens into the stomach. The extremities of other canals have been shewn to possess correspondent sensibilities, or irritabilities, as the two ends of the urethra, and of the common gall-duct. See [IV. 2. 2. 2]. and [4].

The membrane of the upper end of the gullet becomes torpid, and consequently painful, when there is a deficiency of aqueous fluid in the general system; it then wants its proper stimulus. In the same manner a want of the stimulus of more solid materials at the other end of the canal, which terminates in the stomach, produces hunger; as mentioned in Sect. XIV. 8. The proximate causes of both of them therefore consist in deficient irritation, when they are considered as pains; because these pains are in consequence of the inactivity of the organ, according to the fifth law of animal causation. Sect. IV. 5. But when they are considered as desires, namely of liquid or solid aliment, their proximate cause consists in the pain of them, according to the sixth law of animal causation. So the proximate cause of the pain of coldness is the inactivity of the organ, and perhaps the consequent accumulation of sensorial power in it; but the pain itself, or the consequent volition, is the proximate cause of the shuddering and gnashing the teeth in cold fits of intermittent fevers. See Class [I. 2. 2. 1].

Thirst may be divided into two varieties alluding to the remote cause of each, and may be termed sitis calida, or warm thirst, and sitis frigida, or cold thirst. The remote cause of the former arises from the dissipation of the aqueous parts of our fluids by the increased secretion of perspirable matter, or other evacuations. And hence it occurs in hot fits of fever, and after taking much wine, opium, spice, salt, or other drugs of the Art. incitantia or secernentia. The thirst, which occurs about three hours after eating a couple of red herrings, to a person unaccustomed to salted meat, is of this kind; the increased action of the cutaneous vessels dissipates so much of our fluids by insensible perspiration, as to require above two quarts of water to restore the fluidity of the blood, and to wash the salt out of the system. See Art. [III. 2. 1].

M. M. Cold water. Vegetable acids. Warm bath.

The remote cause of sitis frigida, or cold thirst, is owing to the inaction of the cutaneous, pulmonary, urinary, and cellular absorbents; whence the blood is deprived of the great supply of moisture, which it ought to receive from the atmosphere, and from the cells of the cellular membrane, and from other cysts; this cause of thirst exists in dropsies, and in the cold fits of intermittents. The desire of fluids, like that of solids, is liable to acquire periods, and may therefore readily become diseased by indulgence in liquids grateful to the palate.

Of diseased thirst, the most common is either owing to defect of the action of the numerous absorbent vessels on the neck of the bladder, in which the patient makes much paleish water; or to the defective absorption of the skin and lungs, in which the patient makes but little water, and that high-coloured, and with sediment. In both the tongue and lips are liable to become very dry. The former in its greatest degree attends diabætes, and the latter anasarca.

M. M. Warm water, warm wine, warm bath. Opium. Cold bath. Iced water. Lemonade. Cyder.

[2]. Esuries. Hunger has been fancifully ascribed to the sides of the stomach rubbing against each other, and to the increased acidity of the gastric juice corroding the coats of it. If either of these were the cause of hunger, inflammation must occur, when they had continued some time; but, on the contrary, coldness and not heat are attendant on hunger; which evinces, that like thirst it is owing to the inactivity of the membrane, which is the seat of it; while the abundant nerves about the cardia ventriculi, and the pain of hunger being felt in that part, gives great reason to conclude, that it is there situated.

The sense of hunger as well as of thirst is liable to acquire habits in respect to the times of its returning painfulness, as well as in respect to the quantity required to satiate its appetency, and hence may become diseased by indulgence, as well as by want of its appropriate stimulus. Those who have been accustomed to distend their stomach by large quantities of animal and vegetable food, and much potation, find a want of distention, when the stomach is empty, which occasions faintness, and is mistaken for hunger, but which does not appear to be the same sensation. I was well informed, that a woman near Lichfield, who eat much animal and vegetable food for a wager, affirmed, that since distending her stomach so much, she had never felt herself satisfied with food; and had in general taken twice as much at a meal, as she had been accustomed to, before she eat so much for a wager.