SENSES OF SMELL, TASTE, HUNGER AND THIRST 753 



tions and characterize appetite as a pleasurable mental state, which has 

 its origin in an excitation of the mechanisms for taste and smell, while 

 hunger constitutes a more disagreeable and stronger sensation which 

 arises in certain receptors in the walls of the stomach. Carlson^ who 

 has studied this subject more recently, adheres to this classification. 



These general contentions, however, do not aid us very materially 

 in establishing a physiological basis for these sensations; in fact, it 

 must be admitted that we know practically nothing regarding them. 

 Besides the sensory element imparted to them by the senses of smell 

 and taste, they also possess a gastric component introduced by the 

 simultaneous excitation of some sensory unit of the gastric mucosa. 

 Thus, it is a matter of common experience that the ingestion of food 

 blunts the appetite as well as the hunger, while both are evoked by 

 total abstinence. Still, certain conditions may be introduced which 

 lead to a dissociation of these sensations. For example, while a pro- 

 longed fast very frequently diminishes and destroys all the pleasurable 

 sensations connected with the thought of food, the sensation of hunger 

 may persist for some time thereafter. Again, the mere passage of the 

 food through the esophagus may satisfy the appetite, in spite of the 

 fact that the hunger contractions of the stomach continue. Quite simi- 

 larly, the gradual emptying of the stomach after a meal usually restores 

 the appetite at a time when actual hunger is not experienced as yet. 



The contrary sensation of appetite is an aversion to food, which 

 arises whenever the gastric reservoir is well filled or when the body as 

 a whole is unable to assimilate a particular kind of food. Thus, it 

 frequently happens that we acquire an aversion to fat or gelatin in 

 spite of the fact that these substances possess a distinct nutritive value. 

 As in the case of appetite, this sensation arises in special interoceptors, 

 but also embraces a gastric element. 



Hunger. — The sensation of hunger is primarily projected to the 

 region of the stomach, but may also make itself felt by the more 

 general sensations of mental and bodily fatigue and functional de- 

 pression. To begin with, there is a local feeling of emptiness in the 

 stomach which is intensified in the course of time into a painful sensa- 

 tion. Furthermore, this sensation shows a definite intermittency and 

 may be temporarily abolished by the ingestion of even indigestible 

 material. These three facts seem sufficient to disprove one of the hy- 

 pothesis which holds that hunger is a general sensation and is caused by 

 certain changes in the metabolism of the tissues, particularly in that of 

 the nervous tissues. ^ Another view is that hunger is caused by the 

 stimulation of certain afferent nerves in the gastric mucosa in conse- 

 quence of the distention of the glands by accumulated secretion (Beau- 

 mont). No facts can be mentioned in support of this hypothesis other 

 than that sensations of hunger are generally followed by a sudden out- 



1 Carlson and Braafladt, Am. Jour, of Physiol., xxxvi, 1914, 153. 



2 Turro, Zeitschr. fiir. Psych, und Physiol, der Sinnesorgane, xlv, 1911. 



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