SKIN. 93 



to it. It is then placed in some (200 c.c.) of the digesting fluid, which is kept at a temperature 

 of 38 C. in an ordinary water bath for a period varying from three to eight hours, the time 

 depending upon the age and size of the piece of skin. After partial digestion the skin is 

 placed in water for twelve hours, when it swells up and becomes extremely transparent. It 

 may be kept most advantageously in a ten per cent, solution of common salt, or it may be 

 hardened in one of the ordinary hardening fluids, and afterwards stained with logwood or 

 carmine. 



This method is also applicable to other tissues (W. Stirling). 



HUMAN SCALP. 



Vertical Section. EXAMINATION (L). Make the sections parallel with the hair-follicles. 

 Stain a section with picrocarmine or logwood, and mount it in dammar. Observe the 

 epidermis and corium, and in the latter the hair-follicles, each of which gives origin to a 

 hair. Note its mouth, and its bulbous lower extremity, into which projects a vascular papilla. 

 The follicles are usually placed obliquely, and in the scalp they lie in groups of three or 

 four, as is easily seen when a horizontal section is made. Into the upper part or neck of 

 the follicle one or two sebaceous glands open. Rising a short distance above the bulbous 

 portion is the arrector pill, composed of several bundles of non-striped muscle-cells. It runs 

 obliquely upwards through the corium, forming an acute angle with the follicle, and passes 

 over the base of the sebaceous gland, and terminates in a plexus on the surface of the corium. 

 (Indicate a hair-follicle and its muscle in PI. XX II., Fig. i.) 



Study a Hair-Follicle (L and H). Proceeding from without inwards, observe the (i) outer 

 and (2) inner slieath of the hair-sac, which are continuous with the papillary layer of the 

 corium. In the outer layer the fibres 'are arranged longitudinally, whilst in the inner one they 

 are transverse or oblique. Both layers are best marked at the lower bulbous portion of the 

 follicle, where they are pushed into the lower end of the hair, to form a club-shaped papilla. 

 Internal to these two layers is (3) & glassy hyaline membrane, which separates them from the 

 epidermic coverings of the hair. Inside this is (4) the outer root-sheath, which is thickest about 

 the middle of the follicle, and consists of several layers of cells continuous with the stratum 

 Malpighii. Inside this is (5) the inner root-skeath, which in longitudinal sections appears as 

 a thick glassy membrane, though it can be proved to consist of three layers, being from with- 

 out inwards (a) Henle's layer, then (b} Huxley's layer, and (c] the cuticle of the root-sheath, 

 which is a very delicate rnembrane composed of imbricated non-nucleated scales. The inner 

 root-sheath terminates abruptly at the neck of the follicle. Then follows (6) the cuticle of tlie 

 hair and (7) the hair itself. 



Sebaceous Gland (L and H). Observe the duct of one or more of these glands opening 

 into the upper part of a hair-follicle. The membrana propria (of the duct) is continuous with 

 the glassy membrane (3) of the hair-sac, and the epithelium of the outer root-sheath is directly 

 continuous with the epithelium of the duct. The duct after branching opens into flask-shaped 

 or saccular alveoli. In these alveoli are found one or more layers of cells loaded with fat- 

 globules (PL XXII., Fig. 2). 



Arrector pili Muscle (L and H). Observe its attachment to the lower part of the hair- 

 follicle and trace it obliquely upwards towards the surface of the corium (p. 91). It is com- 

 posed of non-striped muscle. 



Horizontal Sections of the Scalp. Stain it with logwood or picrocarmine, and mount it in 

 dammar. Observe the transverse sections of the hairs arranged in groups of three or four. 



