CUTANEOUS AND INTERNAL SENSATIONS 1099 



however, is only another way of saying that the true explanation is 

 still to seek. 



Carlson was unable to confirm the common statement that 

 hunger disappears after the third day of starvation, although there 

 was certainly some decrease in the sensation of hunger, and especi- 

 ally in appetite, on the fourth and fifth days. As has been often 

 shown, the deprivation of food for long periods, or even till death, 

 when water is allowed, is not associated with acute suffering. 



Appetite is distinguished from hunger by those observers who 

 have studied the question most precisely, but of the physiological 

 basis of the sensations that constitute appetite we know even less 

 than we do of the physiological basis of hunger. The taking of 

 food blunts the appetite, as it stills hunger. Fasting evokes both. 

 Yet during a prolonged fast, appetite, the desire for food and the 

 pleasure in the thought or at the sight of it, may disappear, or be 

 much lessened, while the hunger pangs are still sharp. The smell 

 and taste of agreeable food and the mental representations of these 

 sensations are elements in appetite, and even the associations con- 

 nected with the time and place of a customary meal and with those 

 who share it. But there is a gastric element as well: the mere 

 filling of the stomach apart from the passage of nutrient material 

 into the blood helps to satisfy the appetite; the emptying of the 

 stomach in the course of digestion seems of itself to take a part in 

 restoring the appetite for the next meal. To what extent, if at all, 

 the gastric element in the sensation of appetite is dependent upon 

 the same mechanism as the gastric element in hunger is unknown. 

 Some have supposed that the same stimulation which, when its inten- 

 sity is sufficiently increased, causes gastric hunger pains, causes in smaller 

 intensity a milder hunger sensation, which is the gastric factor in 

 appetite. According to Carlson, a factor in appetite is the memory 

 process of removal of hunger pangs by feeding, and he assumes that 

 the revival of such memories in consciousness depends upon the con- 

 dition of the alimentary canal, and is inhibited when the stream of 

 afferent impulses from the viscera is altered by changes in the motility 

 or secretory activity of the gastro-intestinal tract. He believes that 

 the secretion of the so-called appetite gastric juice, in man at least, 

 although clearly demonstrated on a case of gastric fistula during 

 mastication of palatable food, does not possess the great importance 

 attributed to it by Pawlow (p. 404), since normally there is a continuous 

 secretion of gastric juice in the absence of food in the stomach and of 

 psychical stimulation, and this is sufficient to initiate gastric digestion, 

 and therefore to insure a sufficient gastric secretion. The vagi do not 

 seem to contain fibres concerned in the sensations of hunger or appetite. 

 After section of these nerves, dogs, when they survive some time, eat 

 ravenously, although the food is often regurgitated. 



Thirst. This is a sensation, referred chiefly to the pharynx, and 

 certain of the sensory nerve fibres of this region, supplied by the 



