286 ON CUTANEOUS SENSATIONS. [BOOK in. 



of the sensation seems to be a general condition of the body, 

 namely, that produced by the products of digestion ceasing to be 

 thrown into the blood. The sensation is not due to the mere 

 emptiness of the stomach, though the emptiness of the stomach is 

 one of the results of the abstinence from food ; for the feeling of 

 hunger may disappear though the stomach may remain empty, 

 if adequate nourishment be conveyed in other ways, as by 

 injection into the bowels; conversely even we ourselves may 

 under abnormal conditions feel hungry on a full stomach, and in 

 some animals, herbivora, the stomach is always more or less full. 

 The sensation however does seem to be in some way specially 

 connected with the condition of the gastric walls, much in the 

 same way that thirst is specially connected with the palate ; the 

 products of digestion have a much greater power in appeasing 

 hunger when they act locally and directly on the gastric 

 membrane than when they are simply brought to bear on the 

 body at large, and a small quantity of food will immediately 

 satisfy hunger when introduced into the stomach, though it will 

 have no effect when introduced otherwise. Moreover our own 

 consciousness clearly connects the sensation in some way or other 

 with the stomach. 



As to what is the particular change in the gastric membrane 

 which thus gives rise or assists in giving rise to the sensation we 

 know little or nothing; indigestible substances such as cannot 

 be properly called food when taken into the stomach at least 

 temporarily remove the sensation. And we have little or no 

 knowledge as to the particular nerves which serve as the paths 

 for the afferent impulses which we may suppose to be generated 

 in the gastric membrane. Division of the vagus nerve on both 

 sides is said to have no effect on hunger; from this we may 

 conclude that the impulses do not pass up this nerve, though it 

 appears to be the sensory nerve of the stomach. But we have no 

 evidence that the impulses pass along the sympathetic nerves. 



Allied somewKat to hunger is the peculiar feeling which we 

 may perhaps also speak of as a sensation, known as nausea, the 

 precursor of vomiting (see 272) and brought about like vomit- 

 ing by a variety of events. We have little or no knowledge of it 

 viewed as a sensation. 



The affection of consciousness which is produced by the form 

 of cutaneous stimulation known as " tickling " is of a peculiar 

 character, differing from tactile sensations. Indeed it is probably 

 undesirable to speak of it or of other psychical effects of cutaneous 

 stimulation as a sensation, since it seems to be not the direct 

 effect of the sensory cutaneous impulses, which are probably 

 ordinary tactile impulses, but rather the effect on consciousness 

 of changes in the central nervous system brought about by those 

 sensory impulses. 



