EPIDERMAL APPENDAGES. 71 



under the control of the nervous system ; certainly it is no 

 mere filtration dependent only on the amount of blood sent 

 to the surface, for the skin may be hot and dry, particularly 

 in fevers, and a cold sweat may burst out when the surface 

 is pale from deficient flow of blood to the surface, as in the 

 recovery from fainting. 



Considering the function of the perspiration as a moderator 

 of the temperature of the body, the results which are obtained 

 by varnishing the bodies of animals with an impermeable 

 coating are not only interesting, but exceedingly difficult to 

 explain. In such experiments, when the varnishing is com- 

 plete, the temperature rapidly falls, and the animals die after 

 periods varying from a few hours to days; the smaller 

 animals, those in which the total surface bears the largest 

 proportion to the body, being thosa which succumb soonest. 

 Why the temperature falls is not understood ; but whatever 

 the cause of death, such experiments show the importance, 

 in a sanitary point of view, of removing accidental accumu- 

 lations of all kinds from the surface of the body. 



46. Epidermal Appendages. For purposes of protection 

 there occur in different animals a variety of special growths 

 from the cuticle ; and those which occur in the human sub- 

 ject are nails and hairs. 



Fig. 39, NAIL AND ITS MATRIX, longitudinal section, a, Horny 

 layer of epidermis ; &, mucous layer ; c, corium. ... ... 



A Nail is simply a thickening of the outer layer of the 

 cuticle growing from a bed or matrix, which is in the form 

 of a fold at the back part. In this fold there are two sur- 

 faces of skin looking one toward the other, and thus the root 

 of the nail receives additions from above and below, as well 

 as behind. It is pushed continually forwards by new growth 

 at the bottom of the fold, and continues to receive additions 

 to its thickness from the flat part of the matrix as long as it 



