CUTANEOUS AND INTERNAL SENSATIONS. 293 



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. All 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. 



