478 THE SPECIAL SENSES 



stated as follows: As the body or head changes position, 

 the endolymph contained in the various canals and the 

 sacs is subjected to pressure from different points. It 

 thus tends for a given position to press upon definite 

 sensory cells of the sacs and ampuUse. This pressure is 

 transmitted to the brain as an impulse by the nerve fibers 

 attached to these cells, and these impulses enable the brain 

 to become conscious of the relative position of the body, 

 and thus, to exert the necessary control upon the muscles 

 which coordinate movements. The sensitiveness of these 

 sensory cells to such pressure is increased by the presence 

 in the endolymph of the tiny particles of lime (otoliths) 

 which act upon the hairs. This sense of position is often 

 classified as a separate sense, though it is located in the 

 ear. 



Hygiene op the Eak. 



The ordinary injuries to the ear consist mainly of 

 damage to the outer or middle ear. The inner ear is so 

 well protected that it is almost impossible for external 

 causes to affect it. Among the injuries to the outer ear 

 which may be avoided by care is the over-accumulation of 

 ear wax or dirt on the tympanic membrane. Such accumu- 

 lation increases the thickness and destroys the sensitive- 

 ness of the membrane to vibrations. Ear wax allowed to 

 accumulate in this way often hardens, and thus produces 

 deafness. Washing the ear frequently with tepid water will 

 remove the cause and thus prevent this trouble. 



Colds or throat troubles may cause stoppage of the 

 Eustachian tube by mucus or even inflammation of its 

 lining and that of the middle ear. This results some- 

 times in the formation of abscesses, which may be simply 



