CUTANEOUS AND INTERNAL SENSATIONS. 289 



lar material. So also the feeling of satiety and aversion for 

 food that follows overfeeding indicates something more than a 

 simple removal of the sensations of hunger; it impUes an active 

 state, due possibly to the excitation of sensory fibers of a different 

 character. 



The Sense of Thirst. — Our sensations of thirst are projected 

 more or less accurately to the pharynx, and the facts that we know 

 would seem to indicate that the sensory nerves of this region have 

 the important function of mediating this sense. The water con- 

 tents of the body are subject to great changes. Through the lungs, 

 the skin, and the kidneys water is lost continually in amounts that 

 vary with the conditions of life. This loss affects the blood directly, 

 but is doubtless made good, so far as this tissue is concerned, by a 

 call upon the great mass of water contained in the storehouse of the 

 tissues. To restore the body tissues to their normal equilibrium 

 in water we ingest large quantities, and the control of this regula- 

 tion is effected through the sense of thirst. We know little or 

 nothing about the nervous apparatus involved; but it may be 

 assumed that when the water content falls below a certain amount 

 the nerve fibers in the pharyngeal membrane (fibers of the glosso- 

 pharyngeal nerve) are stimulated and give us the sensation of 

 thirst. That we have in this membrane a special end-organ of 

 thirst is indicated, moreover, by the fact that local drying in this 

 region, from dry or salty food, or dry and dusty air, produces a 

 sensation of thirst that may be appeased by moistening the mem- 

 brane with a small amount of water not in itself sufficient to relieve 

 a genuine water need of the body. Our normal thirst sensations 

 might be designated, therefore, as pharyngeal thirst, to indicate 

 the probable origin of the sensory stimuli. Prolonged deprivation 

 of water, however, must affect the water content of all the tissues, 

 and under these conditions sensations are experienced whose quality 

 is not that of simple thirst alone, but of pain or suffering. AH ac- 

 counts agree that complete deprivation of water for long periods 

 induces intense discomfort, anguish, and possibly mental troubles, 

 and we may suppose that under these conditions sensory nerves 

 are stimulated in many tissues, and that the metabolism in the ner- 

 vous system in addition is directly affected by the loss of water.* It 

 is interesting to note that while in diseases due to a general infec- 

 tion, loss of appetite, anorexia, is a frequent symptom, there is no 

 corresponding loss of the sense of thirst. Even in hydrophobia 

 the patient experiences the sensations of thirst, although unable 

 to drink water. 



* According to an interesting account of death from voluntary starvation, 

 quoted by Hertz (loc. cit.), there comes a time at which neither thirst nor 

 hunger causes any distress. 



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