KINESTHESIA 329 



organs is sometimes quite blind without a general notion of the way 

 they are built, while their " function" sometimes is indistinguishable 

 from sensation, even if much more often not. Thus, while we divide the 

 chapter into kinesthesia, vision, hearing, and so forth (functions), our 

 chief concern will be with the organs serving these functions and especially 

 with the ways in which they serve them. 



The senses are special and general. The former have end-organs, 

 nerves, and cerebral centers somewhere or other, probably. The 

 latter arise, in ways unknown at present, more or less throughout the 

 body. 



The order of consideration of the different senses is intended to be 

 that of their probable importance in the conduct of the organism's life, 

 although the positions in the latter part of the list are confessedly 

 arbitrary. We shall discuss kinesthesia, vision, hearing, touch and 

 pressure, taste, smell, the temperature-senses, pain, pleasure, and the 

 general senses, fatigue, thirst, hunger, nausea, and vertigo. 



With these introductory explanations (necessarily different from the 

 preceding parts of the physiology but indispensable as a basis of 

 departure), we shall be in a better position to appreciate the importance 

 of especially the great multitude of afferent organs other than the eyes 

 and ears and taste-buds and smell-cells on which the organism is basally 

 dependent for its activities. 



KINESTHESIA. 



The etymology of this word indicates " the feeling of movement." 

 It includes then the afferent impulses of the organism which are actuated 

 by its movements. These movements are largely produced in the 

 muscles, the tendons, and the joints. We shall discuss first the sense- 

 organs in these parts, because it is becoming yearly more apparent that 

 they have more to do with directing the immediate life of the animal 

 than have any other of the afferent nerve-organs. Their mode of action 

 in connection with the nerve-centers we saw in the chapter on the nervous 

 system and we shall discuss the matter further in relation to the muscles 

 in the next chapter. 



Compared with the great sense-organs of vision and of hearing, these 

 sensory nerve-endings in the muscles, tendons, and joints are simple 

 structures. This may be seen from the accompanying figures. They 

 are, as Huber calls them, the " peripheral teleodendria of dendrites of 

 peripheral sensory neurones." The forms of the nerve-endings already 

 described by histologists are various and consists of two general varieties 

 free and encapsulated. The free endings have not been discovered in 

 muscles or tendons, but they occur in mucosse and in epithelium. 



AFFERENT ENDINGS IN MUSCLE. These are of several forms whose 

 shapes more or less merge into each other. They are probably all 

 actuated by mechanical pressure. 



