272 



THE HVMAN SOD?. 



is called its matrix. Behind, this forms a groove lodging 

 the root of the nail, and it is by new cells added there that 

 the nail grows in length. The part of the matrix lying 

 beneath the body of the nail, and called its led, is highly 

 vascular; new cells formed on its bed and added to its 

 under surface cause the nail to increase in thickness, as it 

 is pushed forward by the new growth at its root. The 

 free end of a nail is therefore its thickest part. If a nail 

 is "cast" in consequence of an injury, 

 or torn off, a new one is produced, pro- 

 vided the matrix is not destroyed.- 



The Glands of the Skin are of two 

 kinds. The sweat glands or sudori- 

 parous glands, and the oil glands or 

 sebaceous glands. 



The Sweat Glands (Fig. 78) are 

 microscopic tubes which reach from 

 the surface of the skin to the subcu- 

 taneous areolar tissue; then the tube 

 often branches, and is coiled up into 

 a little knot, intertwined with blood 

 capillaries. These glands are found all 



' c h MaipigE over the skia > bufc are most abundant on 

 the palms of the hands, the soles of the 

 feet, and the brow. Altogether, there are 

 about two and a half millions of them. 

 The perspiration or sweat poured out by the sudoriparous 



FIG. 78. A sweat 





"What is the matrix of a nail? When does the nail grow longer? 

 "What is the bed of a nail? How does a nail grow thicker? Which 

 is its thickest part? What is necessary in order that a " cast nail " 

 may be reproduced ? 



What glands are found in the skin? Describe a sweat gland. 

 Where are the sweat glands most numerous? How many are there 

 on the whole skin? 



