487 



"when in action. Nerves end in plexuses within the outer layers of 

 the follicle. The mouths of sebaceous glands also open into the upper 

 part of the hair follicles. These glands are situated in the Malpighian 

 layer, and are of a compound saccular form, and lined by cubical 

 cells. 



The thick epidermis protects the underlying structures from the 

 ceaseless frictional contact with the external world, and wards off 

 wounds and invasion by pathogenic organisms. 



The- nails were originally weapons of offence, as well as of 

 defence. 



The hairs shoot off the rain, and keep the body dry. They also, 

 when touched, stimulate organs of sensation. The fur of animals 

 prevents loss of heat by convection. Man developed as a tropical animal, 

 with scanty hair, and endures the cold of the temperate and Arctic 

 climates by fashioning clothes of the hair of animals or fibres of 

 plants. 



The fat of the deep layers protects against heat loss, and also 

 serves as fat depots for the body against times of stress (starva- 

 tion). 



The ceruminous glands of the ear, by the odour and bitter taste 

 of their secretion, are said to prevent insects entering the external 

 ear. 



The sebaceous glands, by their secretion the sebum keep the 

 skin supple, and protect it from the drying effects of the atmosphere, 

 and from the ill-effects of immersion in water. Moreover, pathogenic 

 organisms cannot grow through this secretion. 



The sebum is of a fatty or waxy nature, containing fatty acids, 

 which render it acid, and iso-cholesterin. It is continuously secreted 

 by the sebaceous glands, which occur mainly in the regions supplied 

 with hair, the mouths of the glands opening into the hair follicles. 

 'Tne secretion is squeezed out of the gland by the contractile action 

 of the smooth muscle supplying the base of the hair follicle. 



Sweat Glands. From the stratum Malpighii are developed sweat 

 .glands. These lie in the deeper layer of the corium, and are particu- 

 larly abundant in the palms, soles, forehead, and axillae. There are 

 estimated to be per square inch of skin : 



Forehead . . 



Cheeks . . 



Hand, palm 



Hand, back 



Foot, sole 



Foot, back 



Neck, front and sides 



1,258 



548 



2,736 



1,490 



2,638 



924 



1,303 



^i 



Neck, 



Back 



Buttocks J 



Chest and abdomen 



Thigh, inner surface 



Thigh, outer surface 



417 



1,180 

 57<i 

 554 



The gland proper is situated in the dermis. It consists of a coiled 

 tube, lined with a single layer of secreting cells, arranged upon a 

 basement membrane, on the inner side of which He some smooth 

 .muscle fibres. The ducts are lined with cells in the corium, and form 



