198 PHYSIOLOGY AND HEALTH. 



not this large supply of cutaneous nerves, nor this acute 

 sensibility of the skin. 



467. Underneath this skin there is a layer of fat, which 

 varies in thickness in different parts of the body. It is very 

 thick in the palm of the hand and the sole of the foot, and 

 affords a cushion to meet the pressure that comes upon those 

 or other parts that need this support; while in the forehead 

 and on the back of the hand it is very thin, for there it is not 

 needed. 



CHAPTER III. 



Functions of the Skin . Exhalations : Perspiration. Sensible and 

 insensible Perspiration. Quantity. Experiment at Phoenix Gas 

 Works. 



468. THE skin is the outlet for a good proportion of the 

 waste of the body. Some goes off in the form of carbonic 

 acid, some in the oil, but the greater part in form of perspi- 

 ration. Sanctorius, a celebrated medical writer, carefully 

 weighed himself and all his food, and drink, and excretions, 

 daily, for thirty years; and, after all this observation, he con- 

 cluded that, of every eight pounds which were taken into his 

 system each day, five passed out through the skin. 



469. Seguin, a philosopher, weighed, and then enclosed 

 himself in a bag, which was glazed so as to prevent the per- 

 spiration from passing through it. He found that the largest 

 quantity of perspiration that passed off in a day was four and 

 a half pounds, and the smallest quantity was twenty-four and 

 three quarter ounces ; the medium was thirty-three ounces. 



470. This is the insensible perspiration ; for, although it 

 amounts to about two pints a day, it is not usually percepti- 

 ble; it passes off in such minute portions, and is so com- 

 pletely dissolved in the air, that we do not perceive it. Yet 

 it can be perceived by holding the hand, apparently dry, near 



