94 PRACTICAL HISTOLOGY. 



Make out the different layers of the hair-follicle. Compare also the section of a lip of a 

 dog (p. 60) where these various coverings are exquisitely shown in sections of the large 

 ' feelers.' 



HAIR. 



Human Hair. Pluck a hair from the head, and place its shaft in water. Observe (H) its 

 cuticle, consisting of imbricated scales, then the cortex, which forms the mass of the hair and is 

 composed of horny matter made up of scales, which in pigmented hairs have fine granules of 

 pigment deposited between them. In the centre note the medulla, or pith, which is absent in 

 some hairs (PL XXII., Figs. 3 and 4). A hair may be preserved dry, or simply by adding a 

 drop of dammar solution and then applying a cover-glass, but after the addition of dammar 

 the cuticle is not well seen. 



Hair of Rabbit. Treat it similarly, but note the single or double row of oblong compart- 

 ments in the medulla filled with air, and therefore appearing black. 



Transverse sections of hairs are obtained by shaving, but the hairs of the beard are usually 

 flattened ovals, whilst those of the head are round. 



NAILS. 



Make vertical sections of a nail and its nail-bed after hardening in alcohol or chromic acid 

 and spirit mixture. They are only peculiar modifications of the stratum Malpighii. They 

 rest on very vascular papillae (bed or matrix). 



By steeping them in forty per cent, caustic potash solution, the nails can be resolved into 

 their constituent cells (p. xxxiv). 



BLOOD-VESSELS OF THE SKIN. 



PREPARATION. It is best to employ the skin of the extremities, for a limb is easily in- 

 jected from its main artery. Inject a limb with a carmine-gelatine or Berlin-blue mass. 

 Harden parts of the skin in M Oiler's fluid for two weeks, and then in alcohol. Make mode- 

 rately thick vertical sections. Stain the sections injected with a red mass with logwood, and 

 the others with picrocarmine. Mount them in dammar. It is well to prepare similar sections 

 of an injected scalp, to see the arrangement of the blood-vessels round a hair-follicle. 



EXAMINATION (L and H). Passing from the subcutaneous tissue upwards we find the 

 following systems (Tomsa) : 



(1) Observe the fat-lobules, each supplied by a small artery which forms a dense plexus 

 over and between the individual fat-cells, and from it emerge one or two veins. 



(2) A branch proceeds upwards to the coil of a sweat-gland, where it forms a plexus, 

 whilst the duct is supplied by a branch from an artery in the corium where the capillaries 

 anastomose. 



(3) Each papilla of a hair-follicle receives an arteriole, which splits up into capillaries 

 within it. A plexus of capillaries exists between the outer longitudinal and the inner circular 

 coats of the hair-sac. 



(4) A capillary plexus exists round the sebaceous gland and arrector pili. 



