APPENDAGES OF THE SKIN 131 



removal of a quantity of waste material, or excreta, from the system. 

 Suppression of the function permits an accumulation of effete products 

 in the body, to the detriment of the general health. One of the first 

 effects which follow is the lowering of the temperature, and certain changes 

 in the fibrin of the blood, which is bound to be increased in quantity, 

 and the occurrence of glandular swellings. In the case of animals which 

 have died after being covered with a coat of varnish, it has been found 

 that crystals of the triple phosphate of lime and magnesia are deposited in 

 the cellular tissue and the muscles. Some of the efl'ete products, however, 

 which accumulate under these conditions are eliminated by the kidneys, 

 and these organs consequently become overtaxed and congested, leading 

 to impairment of their function and consequent retention of the urea, 

 which it is their special province to excrete. 



Sebaceous Secretion. — Glands which furnish this secretion are 

 found distributed more or less over the entire body. As we have ex- 

 plained, the majority of them open into the hair follicles, where they 

 discharge their secretion, the use of which is to lubricate the skin and 

 preserve its elasticity and softness. The sebaceous matter consists of 

 two-thirds water, the remainder being fats, extractive matters, a small 

 quantity of albumenoids, and earthy salts. 



Summary. — To sum up the functions of the skin: first in importance 

 is the protection which it affords to the sensitive parts beneath; next, 

 there is its sense of touch, variously developed in different parts of the 

 surface of the body; then its power of perception of the weight and tem- 

 perature of bodies, its use in some degree as an organ of respiration, and 

 finally, its influence as an excretory and secretory structure. 



APPENDAGES OF THE SKIN 



The appendages of the skin are only two in number: i.e. hair, and its 

 modifications in the form of horn, nails or claws. 



Hair. — Hair arises from the bottom of small pits, or follicles, situated 

 in the true skin, in some cases passing completely through it into the 

 tissues beneath (4, fig. 260). Each hair is composed of a bulb, a portion 

 of which is concealed in the follicle, and commonly described as the root, 

 and a free portion or shaft which projects from the surface. The bulb 

 of the hair consists of an aggregation of young epithelium. At its lower 

 extremity it is hollowed out, and fits on to a small papilla at the bottom 

 of the hair follicle. 



Hairs possess a covering of flattened scales or cells arranged, like the 

 outer layer of the cuticle, in the form of tiles on a roof. The outline 



