USES OF THE SKIN 127 



or less rounded or ovoid gland, terminating in a single excretory duct 

 (7", fig. 260). The canal by which the watery secretion is discharged on to 

 the skin as " sweat " takes a somewhat spiral course, which becomes most 

 evident as the tube passes through the epidermis to terminate in a minute 

 opening on the surface. 



USES OF THE SKIN 



Skin as a Protective Covering. — One most olwious function of 



the integument is that of binding the structures beneath it in such a way 

 as to allow freedom of movement, while it keeps them in their relative 

 positions. It varies considerably in its thickness, density, and degree of 

 elasticity in different parts of the body. In the most exposed situations, 

 as the back, it is much thicker and denser than in other parts of the 

 body less exposed to pressure and friction. On the inner surface of the 

 arms and thighs, where it is protected against the forces referred to, its 

 texture is extremely fine, and the hairy covering is either altogether absent, 

 or tne hairs are very sparsely distributed over it. At the bends of joints 

 the presence of a larger number than usual of sebiparous glands renders the 

 skin particularly flexible by virtue of the lubricating action of the secretion 

 which is constantly being poured out by them. The great advantage of 

 this arrangement is rendered all the more evident when anything occurs 

 to disturb it. Any interference with the secretion, or obstruction to the 

 outpouring of the matter secreted, results in the skin in that part becoming 

 dry, scurfy, and inflamed, developing conditions commonly known as chaps 

 and cracks. On the other hand, in certain disordered states the secretion 

 may be formed in excess of that which is required, when it constitutes the 

 disease termed " grease ". 



Skin as an Organ of Touch. — The skin is described commonly as 

 an apparatus of touch, a sense which resides in a special manner in the 

 terminal parts of the extremities and the lips. It is, however, distributed 

 more or less over the whole surface, varying in acuteness in different parts 

 of the body. Dr. Carpenter refers, in his Principles of Physiology, to 

 the researches of Prof E. H. Webber and Dr. Ballard in reference to the 

 relative sensitiveness in different parts of the skin. One test was that 

 of employing the legs of a pair of compasses, the points of which, 

 guarded with pieces of cork, were brought together as close as possible, 

 until the smallest distance at which they could be felt to be apart from 

 one another was reached. This was termed by Dr. Graves as the limit 

 of confusion. A table is given, showing the limit of confusion, from 

 which the following instances are taken. In the first place, the point of 



