36 HUMAN PHYSIOLOGY 



parts are diseased, as in locomotor ataxia (see page 229), 

 disturbances in the movements occur. 



It is supposed by many authors that muscular sensations 

 are due to the fact that we are conscious of the degree of 

 innervation of the motor nerve in the central organs. 



There are still a number of organ sensations which are of 

 such an indefinite character that at present little can, with 

 certainty, be said about them. The knowledge concerning 

 them is diminished by the fact that they are often accom- 

 panied by strong feelings (bonheur and ennui) by which their 

 quality is masked. They are generally called common sen- 

 sations and include hunger, thirst, itching, tickling, shudder* 

 ing, fatigue, pleasure, ennui, giddiness, etc. 



Of special physiological interest are the organ sensations, 

 hunger and thirst, as they call for the partaking of solid and 

 liquid food. The sensation of hunger is the sensation of an 

 empty alimentary canal, which disappears even when the 

 stomach is filled with an undigestible substance. In the 

 sensation of hunger the sensory nerves of the stomach and 

 intestine seem to play a part. If the period of hunger is 

 long continued, an undefinable sensation of general need of 

 food is present. 



Thirst is the sensation produced by dryness of the pharynx, 

 which disappears when the mucous membrane of the palate 

 and the pharynx is moistened. Hence the sensation of 

 thirst is produced by the stimulation of the sensory nerve .of 

 the mucous membrane by drying. 



