HUNGER 137 



The five will be listed, and each considered briefly. They 

 are the organs of hunger, thirst, pain, muscle sense, and 

 equilibrium. 



Hunger. — This is a sense whose biological importance 

 is manifest, since without it animals would not be driven 

 to the search for and consumption of food, and so would 

 starve to death. When one realizes that of all animals 

 man only has learned the connection between the taking 

 of food and the avoidance of death by starvation, he can 

 appreciate the importance of the mechanism which impels 

 animals to eat. The organ for hunger in man and in the 

 higher animals is located in the wall of the stomach, and 

 is stimulated by a particular kind of muscular contraction 

 in the stomach wall which gives rise to what is known 

 as a pang of hunger. The sense of hunger is complicated 

 by the thing we call appetite, which is not a true sense, 

 as is hunger, but is rather a memory of the enjoyment of 

 food. We do not know much about the relation of appe- 

 tite to hunger in any of the lower animals, but in our- 

 selves we recognize that appetite has a good deal to do 

 with arousing genuine hunger. In thinking of hunger, 

 and of appetite, one has to remember that civilized man 

 has gone a long way in his habits from his savage pro- 

 genitors, and the conditions for arousing the sense of hun- 

 ger are correspondingly altered. We know that all kinds 

 of animals which have to rove about in search of food 

 are impelled urgently to that search by some means. At 

 present it is not known whether that means consists, in 

 such lower forms as insects, for example, of an organ of 

 hunger in the stomach, though such an organ is present 

 in mammals and probably in birds. 



Thirst. — This is the sense which impels land animals 

 to take water from time to time for the purpose of re- 

 placing that which is lost from their bodies by evapora- 

 tion and through the channels of excretion. In man, 

 and probably also in the higher animals, the organ of 

 thirst is located in the mucous lining of the throat, and 



