286 THE SPECIAL SENSES. 



or of the joints or limbs moved by them. It includes also the 

 sense of passive position, and the sense of effort and of the spatial 

 relations of the limbs in motion or at rest. When the afferent 

 fibers from the muscles and joints are traced into the central 

 nervous system, some of them, it will be remembered, enter the 

 tracts of Flechsig and Gower and end in the cerebellum, while 

 ucuers pass up the cord in the posterior funiculi, enter the lemniscus, 

 and terminate eventually in the cerebral cortex in the post- 

 Rolandic region. Our conscious muscular sensations are mediated 

 presumably by this latter group. The untrained person scarcely 

 recognizes the existence of these sensations, but they are evident 

 enough upon analysis, and it is most certain that they take a 

 fundamental part in regulating our movements. In our estima- 

 tions of the extent of the muscular contractions they form the 

 chief sensory basis, and in this way they may indirectly furnish 

 us with data for perceptions and judgments of various kinds. 

 Doubtless, also, this sense takes an essential part in the primitive 

 formation of our conceptions of space, since it may be assumed 

 that the continual movements of the extremities furnish in con- 

 nection with our visual and tactile impressions essential data 

 upon which we build our perceptions of distance and size, our 

 judgments of spatial relations. As is explained in the chapter 

 on the Physiology of the Ear, the sensations from the semi- 

 circular canals and vestibular sacs co-operate in giving data for 

 these fundamental conceptions, and it is not possible for us to 

 disentangle the parts taken by these senses separately in building 

 up our knowledge of the external world. 



Sensations of Hunger and Thirst. — Hunger and thirst are 

 typical interior (or common) sensations. We feel them as changes 

 in ourselves, although the sensations are of such a vague character 

 that it is difficult to analyze them successfully by methods of intro- 

 spection. The feeling that we designate commonly as hunger or 

 appetite occurs normally at a certain time after meals, and it is 

 referred or projected more or less definitely to the region of the 

 stomach. When the sensation is not satisfied by the ingestion of 

 food, it increases in intensity and the individual experiences the 

 pangs of hunger. The testimony of those who have starved for 

 long periods, as well as the experience of professional f asters, indi- 

 cates that these pangs after a few days diminish in strength and may 

 finally disappear, so that prolonged starvation is not accompanied 

 necessarily by physical suffering. The older observers made a 

 distinction between a hunger supposed to be due to conditions in 

 the stomach and a hunger due to insufficient nutrition in the body 

 at large. Whether or not sensations of this quality can arise from 

 impoverished nutrition of the tissues in general has been a matter 

 of some dispute. There are some facts which indicate that a 



