52 THIRST. 



therefore be subject to the common laws of sensation. Hence 

 uncivilised tribes enable themselves to traverse large tracts with- 

 out food by swallowing pills containing tobacco or opium. The 

 pain of all excessive muscular contraction is lessened by pressure; 

 whence the uneasiness of hunger is lessened by a belt fixed tightly 

 over the stomach; and some Northern Asiatic tribes really place 

 a band there, and lace it behind with cords drawn more tightly, 

 according to the degree of the uneasiness. Thus, too, the state of 

 the stomach remaining the same, hunger may diminish from the 

 occurrence of other feelings which attract our attention more 

 forcibly, by passions of the mind, &c.: as is exactly the case with 

 all other sensations, even with those that are morbid. Under 

 strong attention of the mind to pursuits of either intellect or 

 passion, to delightful or painful sensation, all other feelings cease 

 to be felt, although really violent; and frequently, from being 

 unattended to, do not recur. Passions, however, and the narcotic 

 pills of savages, may affect hunger, not only by increasing or di- 

 minishing the sensibility to the state of the stomach, but by in- 

 creasing or diminishing this state the cause of the sensation. 



As hunger appears to depend upon the local condition of the 

 stomach, so does thirst more evidently upon that of the mouth 

 and fauces. Every consideration renders it probable that thirst is 

 the sensation of the deficiency of moisture in the parts in which it 

 is seated. Whatever produces this, either by causing the fluids of 

 the mouth and fauces to be secreted in small quantity or of 

 great viscidity, or by carrying off the fluid when secreted, pro- 

 duces thirst ; and vice versa. To be dry means to be thirsty, be- 

 cause the state is removed by directly wetting the parts, or by 

 supplying the system with fluid, that they may be moistened by 

 their own secretions. Being a sensation, the same may be re- 

 peated in regard to it as was observed respecting hunger. Rage 

 or terror dry up the mouth and throat, and cause violent thirst. 

 Thirst is only momentarily assuaged by wetting the mouth and 

 throat, because they presently grow dry again. Fluids must be 

 swallowed to be effectual, that they may be absorbed and the 

 part thus preserved moist by constant secretion. 



" The necessity of obeying those stimuli is greater or less, ac- 

 cording to age, constitution, and especially according to habit, 

 and nothing can therefore be affirmed positively respecting its ur- 

 gency ; but a healthy adult, in whom all the calls of nature are 



