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Major W. B. Cannon. 



of his yearning. And the common acquaintance of mankind with the potent 

 demands of hunger and thirst for satisfaction renders these similes easily 

 understood. 



In undertaking a discussion of thirst it is necessary at the start to distin- 

 guish clearly between the primitive sensation itself and appetite. The same 

 distinction had to be drawn in considering the nature of hunger. The 

 hunger pang is a disagreeable ache or gnawing pain referred to the lower 

 mid-chest region or the epigastrium. Appetite for food, on the other hand, 

 is related to previous experiences which have yielded pleasurable sensations 

 of taste or smell. Thus associations become established between particular 

 edible substances and the delights tliey convey, with the result that a wish 

 develops that the delights may be renewed. In either circumstance, whether 

 for the satisfaction of appetite or for tlie satisfaction of hunger, the body is 

 supplied with food. 



Similarly in the case of drink, the appetite for this or that peculiar potable 

 substance develops from former experience and from established associations 

 of an agreeable character. We drink not only because we are thirsty, but 

 also because we relish a certain aroma or bouquet, or a peculiar taste, and 

 wish to enjoy it again. In respect to appetite the taking of fluid differs from 

 the taking of food, in that fluid, which leaves the stomach rapidly, may not 

 occasion a sense of satiety as does food, which accumulates in the stomach. 

 In this possibility of continuing pleasurable sensations associated with 

 drinking lie the dangers that arise from the excessive use of beverages. 

 Under normal conditions, however, it is through the satisfaction of appetite 

 for a particular drink, e.g., for tea, or coffee, or light alcoholic beverages, 

 that the body may be supplied with sufficient water for its needs before 

 thirst has had occasion to manifest itself. But just as there is provided, back 

 of the appetite for food, in readiness to become imperious if necessary, the 

 sensation of hunger ; so likewise, as a final defence against a too great 

 depletion of the water content of the body, there may appear the urgent and 

 distressing sensation of thirst. 



There is a general agreement that thirst is a sensation referred to the 

 mucous lining of the mouth and pharynx, and especially to the root of the 

 tongue and to the palate. McGee, an American geologist of large experience 

 in desert regions, who made numerous observations on sufferers from 

 extreme thirst, has distinguished five stages through which nien pass on 

 their way to death from lack of water.* In the first stage there is a 

 feeling of dryness in the mouth and throat, accompanied by a craving for 

 liquid. This is the common experience of normal thirst. The condition 

 * McGee, ' Interstate Med. Jour.,' vol. 13, p. 279 (1906). 



