54 



A COURSE ON ZOOLOGY. 



.* 29. 



apple ably painted on canvas could deceive our eyes and 



make us believe that the fruit 

 was actually present. If all 

 our means of perception our 

 organs of sense were absent, 

 the apple would disappear, 

 and for us would cease to 

 exist. 



In the physiological exam- 

 ination of the functions of 

 sensation in man, we must 

 consider five distinct appa- 

 ratus, serving as the instru- 

 ments of five distinctly char- 

 acterized series. These are 

 8 touch, taste, smell, hearing 1 , 

 and sight, 



Touch. The sense of touch 

 notifies us of the contact of 

 other bodies with our per- 

 sons; it gives us many no- 



VEKTICAL SECTION OF THE SKIN OF tions concerning; the different 



THE FOREFINGER ACROSS TWO OF . 



THE RIDGES OF THE SURFACE physical properties and con- 



(highly magnified).-!, dermis, ditions of bodies, SUCh as 

 composed of an intermixture of 



bundles of fibrous tissue ; 2, epi- orm > dimensions, consistence, 



dermis; 3, horny layer; 4, soft elasticity, Weight, tempera- 

 layer; 5, subcutaneous connec- T , 



tive and adipose tissue; 6, tactile ture > etc - ln man the 8en Se 



papillae; 7, sweat-glands; 8, duct; of touch exists more Or less 



9. spiral passage from the latter -, -, i .1 , . 



through the epidermis; 10, ter- developed over the entire sur- 



mination of the passage on the face of the skin. 

 summit of ridge. 



The skin ig composed of twQ 



layers, the epidermis and the derm. The epidermis is 

 the external layer ; it is formed of superposed layers of 



