210 THE HUMAN BODY 



definite sense aroused in a specific manner. In consciousness it 

 takes the form of sensations arising from the stomach, which, when 

 pronounced, are of a character sufficiently disagreeable to justify 

 their description as " pangs of hunger." During a period of hunger 

 the feeling is not continuous, but comes and goes, usually at fairly 

 regular intervals. By means of interesting experiments, in which 

 records were obtained of the movements of the stomach, the fact 

 was demonstrated that spasms of hunger are the result of vigorous 

 contractions of the muscular walls of the organ. Apparently these 

 contractions stimulate, mechanically, receptors embedded in the 

 stomach walls. Most of the facts about hunger are readily ex- 

 plicable in accordance with this idea of its nature when we recall 

 that the stomach, whose contractions evoke the sensations, is 

 governed by the autonomic system, which, in turn, is subject to 

 emotional as well as to reflex influences. The well-known capri- 

 ciousness of hunger can thus be accounted for. If the need for 

 food were the necessary incitement to hunger we should expect 

 the greatest hunger to be after the longest fast, but the experience 

 of a great many people is that their least hunger before any meal is 

 before breakfast, which is the meal at the end of the longest inter- 

 val. Moreover, those who have endured long fasts testify that 

 hunger disappears completely after a period of two or three days, 

 particularly if not much exercise is taken. 



The function of hunger is to insure the taking of food. This 

 is an act essential to life, but in the lower animals, and in children, is 

 not recognized as such through the operation of associative mem- 

 ory, and, therefore, is not to be depended on to be performed 

 volitionally. It is essentially a reflex act and hunger is the sensory 

 basis for the reflex. As we shall learn in a later chapter, an im- 

 portant feature of proper eating is the maintenance of regular 

 habits in regard to it. Hunger serves as a powerful aid to regular- 

 ity, for it tends to come on at about the time we are in the habit of 

 eating. Many people suffer rather severely if obliged to wait 

 through the period of a usual meal, although the interval measured 

 in hours may be no longer than others to which they are accus- 

 tomed and which cause no discomfort. 



Thirst. This sense, in its ordinary form, arises from dryness of 

 the throat. Apparently there are receptors in that region whioh are 

 stimulated by deficiency of moisture. The throat is moistened by 



