CHAP, vi.] SOME OTHEE SENSATIONS. 1049 



fistula water is introduced into the stomach through the fistulous 

 opening, large quantities may be given before thirst is assuaged. 



The sensation of hunger is in a somewhat similar manner re- 

 ferred to, or associated with, the condition of the gastric mucous 

 membrane. We feel hungry when the stomach is empty. But 

 even more distinctly than in the case of thirst the main cause 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 ade- 

 quate nourishment be conveyed in other ways, as by injection 

 into the bowels; conversely even we ourselves may under ab- 

 normal 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 mem- 

 brane 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 con- 

 sciousness 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 con- 

 clude that the impulses do not pass up this nerve, though it ap- 

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

 evidence that the impulses pass along the sympathetic nerves. 



Allied somewhat to hunger is the peculiar feeling which we 

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

 precursor of vomiting and brought about like vomiting 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 prob- 

 ably undesirable to speak of it or of other like psychical effects 



