QUESTIONS 245 



sensations occupy the border line between common sensibility 

 and the special sense of touch, such as tickling and itching. 

 Pain points are separate from pressure points and are more 

 numerous. More than 100 are found to every square centimeter 

 of the skin, and they require 1000 times as great a stimulus for 

 their excitation as do the pressure points. 



Hunger and thirst are peculiar sensations, which ordinarily 

 depend partly on local and partly on general causes. Local 

 causes of hunger and thirst are an empty stomach and certain 

 conditions of the mucous membrane. These sensations are 

 felt largely as the result of habit, and depend thus upon the 

 condition of secreting and absorbing mechanisms. 



By taking a body in the hand and rasing it, a sense of resist- 

 ance is felt in the muscles, by the intensity of which the weight 

 of the body can be determined more accurately than by the 

 pressure sense alone. This is called muscular sense. It is 

 developed to an exceedingly fine degree in some occupations; 

 for example, postal clerks detect overweight letters with [won- 

 derful accuracy and quickness. Muscular sensation is allied 

 closely to touch sensation. It is due to the inflow of sensory 

 impulses which indicate the tension to which the muscle has 

 been subjected. The latter view is corroborated by the exist- 

 ence of sensory endings, the muscle spindles, in muscles and 

 tendons. 



QUESTIONS ON CHAPTER XIII 



What are the functions of the eye? 



Give the essential parts of the eye. 



What are primary, secondary, and tertiary positions of the eye? 



How is an image formed on the retina? 



Discuss accommodation. 



Discuss the effect of drugs on accommodation. 



Give the nervous mechanisms of accommodations. 



Define near and far points and the range of accommodation. 



What is an emmetropic eye? 



Discuss myopia and hypermetropia. 



What are presbyopia and astigmatism? 



Discuss diplopia of the eye. 



Define spherical aberration and chromatic aberration. 



Give the nervous mechanisms that control the iris. 



Discuss intra-ocular images. 



Why does the pupil appear black? 



What is an ophthalmoscope? 



What are the most important structures of the retina? 



What are the blind spot, macula lutea, and fovea centralis? 



