200 ANSWERS TO PRACTICAL QUESTIONS 



of thought by conventional signs. Hearing is a necessary con- 

 dition of articulate language ; without it man lives alone, affec- 

 tion and confidence lose their most precious forms of expression, 

 and friendship can not exist. Auditory sensations act upon the 

 nervous system with more force than visual sensations. We 

 are carried away by rhythm, or it adapts itself to our ideas 

 and our passions ; music plunges us into an ideal world, and 

 holds us by an indefinable charm ; in a word, if sight speaks 

 more especially to the intellect, hearing addresses itself to the 

 affections. Sight is certainly more necessary to man than hear- 

 ing, but still the blind are generally gay and communicative, 

 while the deaf seem inclined to melancholy. As to the relative 

 influence of these two senses on the development of the intel- 

 lect, we know that the education of the deaf is slow, but may 

 be complete, while that of the blind is, on the contrary, rather 

 rapid, but is almost always very limited ; many ideas can not 

 be acquired by them, and, as has been remarked by M. Longet, 

 their minds rarely attain maturity." 



17. Which coat is the white of the eye ? 



The sclerotic. 



18. IVJiat makes the difference in the color of eyes ? 



The varying shade of the pigment deposited in the iris of 

 the eye. 



19. Why do we snuff the air when we wish to obtain a 

 distinct smell? 



As muscular actions are called into play to aid the sense of 

 taste, as in smacking the tongue and lips, so the act of "sniff- 

 ing," which is a mixed respiratory and nasal muscular effort, 

 is used to bring odorous substances more surely and extensively 

 into contact with the upper and proper olfactory region of the 

 nose, besides causing a larger amount of them to pass over the 

 mucous surface in a given time. MARSHALL. 



20. IVliy do red-hot iron and frozen mercury (40) 

 produce the same sensation ? 



The sensation in both cases is that of pain, not that of 

 touch. 



