74 ANIMAL PHYSIOLOGY. [LESSON 25. 



408. There is yet another plan, superior in some of its effects to all 

 that has preceded it ; at night, when you go to bed, and whenever you 

 get out of bed during the night, spend from two to five minutes rub- 

 bing your whole body and limbs with your hands, as far as you can 

 reach in every direction ; let it be done briskly, quickly, and hard. 

 By this practice the softness and mobility of the skin will be pre- 

 served, which too frequent washings has a tendency to destroy. 



409. The cuticle has neither nerves nor blood-vessels, but it is 

 abundantly pierced by the evacuating ducts of the sebaceous (fatty) 

 and sudoriferous (sweat) glands, and also by the shafts of the hairs. 



410. It appears to be developed for the sole purpose of protect- 

 ing the layer beneath it the true skin. 



411. If the cuticle be accidentally removed, the true skin suf- 

 fers acute pain from exposure to the air, and change of temperature. 

 In addition to the cells of the epidermis whose function it is to secrete 

 horn, there are other cells secreting only pigment (paint) ; in the white 

 races of mankind these cells are easily distinguished, but they are 

 most apparent in the colored races. There appears to be great 

 relation subsisting between the development of pigment cells in man, 

 and exposure to light, that is to say, the greater the light, the more the 

 color. It is under circumstances of intense heat and light, that the 

 negro, the red Indian, and all the varieties of the colored races of 

 mankind, are produced and nourish. In this respect the analogy 

 with plants is no less perfect than admirable. 



LESSON XXY. 



THE NAILS. 



412. May be regarded as an altered, transformed, or modified 

 epidermis ; they consist of two layers a soft mucous and the horny 

 layer, or true nail. 



413. The bed, or matrix of the nail, corresponds with it accu- 

 rately in size and form. If the nail be removed by maceration, its 

 anterior (front) and middle portions are divested of epidermis, and 

 become uncovered ; the lateral portions, or edges, and the posterior 

 portion (back part) are invested by a part of the cutis. This will be 

 best understood by consulting the accompanying figure (Fig. 110), 

 which gives a view of a transverse section of a nail, made through 

 the body and bed of it. The bed of the nail (with black ridges) is 



