198 RECEPTORS 



chemist works in an atmosphere which causes his visitor to choke 

 and splutter, but the introduction of a new odour, say ammonia, 

 is at once perceived and produces instant action. 



Hunger is a sensation which must be regarded as primitive and 

 basal. It is not our business to analyse the feelings of hunger, 

 but to consider the mechanism by which the lack of nourishment 

 is signalled to consciousness. The evolution of knowledge of this 

 sensation is largely due to Prof. Cannon, whose book on the subject 

 should be read by every student. There can be no doubt that the 

 feeling of hunger is closely allied to pain. 



" The sensation of hunger is difficult to describe, but almost 

 everyone from childhood has felt that dull ache or gnawing 

 referred to the lower mid-chest region or epigastrium, which takes 

 imperious control of human actions. As Sternberg has pointed 

 out, hunger may be sufficiently insistent to force the taking of 

 food which is so distasteful that it not only fails to rouse appetite 

 but may even produce nausea. The hungry being gulps his 

 food with a rush. The pleasures of appetite are not for him he 

 wants quantity rather than quality, and he wants it at once 



Hunger may be described as having a central core and certain 

 more or less variable accessories. The peculiar dull ache of 

 hungriness referred to the epigastrium is usually the organism's 

 first strong demand for food ; and when the initial order is not 

 obeyed, the sensation is likely to grow into a highly uncomfortable 

 pain or gnawing, less definitely localised as it becomes more 

 intense. This may be regarded as the essential feature of hunger. 

 Besides the dull ache, however, lassitude and drowsiness may 

 appear, or faintness, or violent headache, or irritability and rest- 

 lessness such that continuous effort in ordinary affairs becomes 

 increasingly difficult. That these states differ much with 

 individuals headache in one and faintness in another, for, 

 example indicates that they do not indicate the central fact of 

 hunger, but are more or Jess inconstant accompaniments. The 

 ' feeling of emptiness,' which has been mentioned as an important 

 element of the experience, is an inference rather than a distinct 

 datum of consciousness and can likewise be eliminated from 

 further consideration. The dull pressing sensation is left, there- 

 fore, as the constant characteristic, the centra] fact to be examined 

 in detail " (Cannon). 



Cannon and his colleagues have definitely proved that the 

 sensation of hunger is caused by strong contractions of parts of 

 the alimentary canal. As we shall see later when dealing with 



