144 URINARY APPARATUS. 



Hair. With reference to the structure of hair, it is of im- 

 portance to notice that each follicle consists of a connective 

 tissue layer, and of a layer of muscular fibres. The former, 

 which is richly supplied with capillaries, is formed of fibres 

 which run mostly longitudinally, and seem to be merely a con- 

 densation of the surrounding tissue. In certain parts, this 

 layer is in immediate contact with the external hyaloid mem- 

 brane of the hair; in others, there exists between them a cir- . 

 cular layer of plain muscular fibres, which varies in distinct- 

 ness in different varieties of hairs, but is always most strongly 

 developed in the neighborhood of the bulb. In the eyelash of 

 the mature foetus, the muscular layer is much stronger than 

 the connective tissue layer, and can be traced over the whole of 

 the bulb. As regards the structure of the hair itself, all that 

 is required will be readily understood from the description 

 given in the ordinary text-books. 



The structural facts relating to the root of the hair can be 

 easily made out in chromic acid preparations. The structure 

 of the shaft can be best seen by preparing fresh hair (of the 

 scalp) in concentrated acetic acid, by which means the cuticle 

 and the elements of the medulla are brought into view. For 

 the isolation of the plates of the cuticle, and of the fibre-cells 

 of the substance of the hair, concentrated sulphuric acid is 

 used, at a temperature of 40 to 50 C., in which the hair must 

 be heated for about an hour. After steeping for several days 

 in two per cent, solution of caustic potash, the elements of the 

 medulla become very distinct. The development of the hair, 

 and of the sweat glands and sebaceous glands, may be studied 

 in embryos at various periods, in preparations hardened with 

 chromic acid. The most important point to notice is, that in 

 mature embryos, or even in the eyelashes of children, if the 

 section coincides precisely with the axis of the hair and involves 

 the papilla, it is seen that that part of the external l^aline mem- 

 brane which extends over the papilla is uninterruptedly covered 

 with the regularly arranged cells of the external sheath, and 

 that these cells occupy the whole bulb to about half-way up 

 the root. It is common to find several stages of development 

 in a single preparation, from which it can be learnt that the 

 new hair takes its origin from the axial cells of the sheath of 

 the root, being formed by the lengthening of these elements. 



SECTION II. URINARY APPARATUS. 



Epithelium of the Kidneys. For the study of the epi- 

 thelium of the kidneys, the pig, dog, or mature foatus may be 

 used. The fresh kidneys having been divided into two halves, 

 in the direction of the length of the organ, juice from the cut 

 surface may be employed for the study of the epithelium of 



