THE SENSES. 



519 



The sense of smell, which is only moderately developed in man, is 

 very acute in many animals. The dog will not only discover game 

 and follow it by the scent, but will distinguish individuals by their 

 odor, or recognize articles of dress belonging to them by the minute 

 quantity of odoriferous vapor adhering to the fabric. 



Sense of Sight, 



This is the most remarkable of all the senses, both for the special 

 nature of its impressions, the complicated structure of its apparatus, 

 and the variety and value of the information which it affords with 

 regard to external objects. It is by this sense that we receive impres- 

 sion? of light and color, with all their modifications of intensity and 

 combination, and acquire our principal ideas of form, space, and 

 movement. The eye is equally sensitive to the impressions of light, 

 whether it come from near or remote objects, or even from the immeas- 

 urable distances of the fixed stars. It is superior to the other organs 



FIG. 130. 



HORIZONTAL SECTION OF THE RIGHT EYEBALL.!. Optic Nerve. 2. Sclerotic coat. 3. Cornea. 4. 

 Canal of Schlenini. 5. Choroid coat. 6. Ciliary muscle. 7. Iris. 8. Crystallite lens. 9. Retina. 

 10. Hyaloid membrane. 11. Canal of Petit. 12. Vitreous body. 



of sense in its rapidity of action, and in the delicacy of the distinctions 

 which it is capable of making in the physical Dualities of external ob- 

 jects ; and it affords the most continuous and indispensable aid for all 

 the ordinary occupations of life. 



Organ of Vision. The eyeball consists of a spheroidal fibrous sac, 

 the sclerotic coat (Fig. 130, 2 ), filled with fluid find gelatinous mate- 

 rial, provided anteriorly with a transparent portion, the cornea G), and 



