i7o PHYSIOLOGY FOR BEGINNERS CHAP, 



the epidermis. No blood-vessels run into the epidermis itself. 

 The dermis is well supplied with nerves. Some of these end 

 in peculiar round or oval structures in some of the papilla", as 

 well as in the deeper parts of the dermis. Very fine fibrils 

 from some of the nerves pass into the epidermis and end there 

 in the deeper layers. Most of these nerve fibres are for con- 

 veying to the brain nervous impulses arising in the skin, which 

 lead to such sensations as touch, temperature, and pain. They 

 will be considered more fully in connection with the special 

 senses. 



The Glands of the Skin. If the skin of the palm 

 of the hand is examined with a lens, a row of pits or 

 depressions will be seen on the ridges. These are the pores 

 or openings of the sweat glands. Each pore leads by a 

 spiral or corkscrew-like tube through the epidermis into the 

 dermis. In the dermis the tube, the wall of which is here 

 formed of a single layer of cubical cells, is continued down 

 to the deeper part of the skin, and there its blind end becomes 

 coiled into a kind of knot. This coiled part is a sweat gland. 

 The cells are larger in the coiled part of the tube than else- 

 where, and among the coils are numerous blood-vessels. These 

 cells secrete from the blood the sweat, which is then conducted 

 along the tube to be discharged on the surface of the skin. 

 Minute droplets of sweat can with a magnifying glass be often 

 seen at the separate pores. 



Other glands, namely the sebaceous glands, are present 

 in the skin, and are also situated in the dermis. They are 

 much smaller than the sweat glands, and are always connected 

 with hairs. Each consists of a short duct leading to a small sac 

 lined with and indeed filled with cells. The duct opens into 

 the depression in the skin or follicle, as it is called, in which 

 a hair lies. The secretion is fatty in nature. 



Composition and Secretion of Sweat. The sweat or 

 perspiration consists of water containing a very little dissolved 

 solid matter. This is composed chiefly of common salt and 

 certain organic bodies of an acid or fatty nature. Some 

 carbonic acid is present. The perspiration is alkaline, but 

 when it is mixed with the sebaceous secretion may be acid. 



Usually the perspiration is secreted in small quantity, and 

 then evaporates into the air from the pores of the ducts. Such 



