94 EPIDERMIS. [SECT. 49. 



During embryonic life repeated desquamations of the epidermis take place. 

 This can be demonstrated with ease in the second half of intra-uterine life, 

 when the process is very energetic. From the fifth month onwards, especially, 

 the casting off of the outermost epidermic cells continues in an increasing 

 degree ; and as they become in most places intermingled with the sebaceous 

 matter of the skin, which begins to be excreted at this period, they form the 

 so-called smegma cmbri/onum, or vernix cascosa. This is a whitish or yellowish, . 

 inodorous, greasy substance, which, especially from the sixth month onwards, 

 covers the entire surface of the foetus with a considerably thick, or even 

 stratified coating. It is found in large quantities on the genitals, the flexion- 

 side of the joints (axilla, knee, inguinal region), the sole of the foot, the palm 

 of the hand, the back, ear, and head. Microscopically examined, it is seen to 

 consist principally of epidermis-cells, with cells from the sebaceous follicles 

 and globules of fat. Two or three days after birth, the smegma is thrown off 

 and the permanent epidermis makes its appearance, the further changes of 

 which are but little known. In the child of four months of age, the epidermis 

 is disproportionally thick, which especially depends upon the mucous layer, 

 whilst the horny layer is only slightly developed. The pigment of the mucous 

 layer, as well in the coloured races as in Europeans, is developed after birth ; 

 but in the former (the negro) the margins of the nails, the areola of the 

 nipple, and the genital organs become coloured about the third day, and on 

 the fifth and sixth day the colour is diffused over the whole body. 



In examining the skin, perpendicular and horizontal sections of fresh, dried 

 or boiled preparations, moistened with an inactive fluid, or with various 

 agents, as acetic acid and alkalies, are of service. The most important effects 

 of these re-agents have been already mentioned in their proper place. The 

 epidermis can be separated from the corium, easily and in large patches, by 

 maceration or boiling ; and, when it is not thick (on the genitals, for instance), 

 also by acetic acid and soda, so that its lower surface and the papillae of the 

 corium are exhibited most beautifully, and the latter can be investigated 

 isolated or in groups. In the fresh skin, their position and number can be 

 quickly and easily ascertained in horizontal sections," carried through the 

 papillae and the deep layers of the epidermis. The vessels -may be studied in 

 thin parts of the skiD (genitals and lips) in the fresh condition, or in injected 

 preparations. The nerves may be examined in perpendicular sections, in 

 isolated papillae, or in thin parts of the skin (prseputium, glans, eye-lids, or 

 conjunctiva bulbi), after addition of acetic acid and diluted soda, or according 

 to Gerber's and Krawses method. Gerber boils the skin until it becomes 

 transparent, lays it for a few hours in oil of turpentine until the nerves are 

 white and shining, and then examines them in fine perpendicular lamella), 

 made with the double knife. According to Krause, the nerves may be seen 

 very well by treating the skin with nitric acid, when the proper degree of 

 action is hit upon. The elastic tissue is shown very beautifully by acetic 

 acid, soda, and potass. The smooth muscles can be with facility isolated in the 

 tu idea dartos, with more difficulty in the skin of the penis and areola of the 

 nipple, where the observer must be familiar with them, in order in all cases 

 to discern them with the unaided eye. On the hair-follicles they are to be 

 seen under the microscope, when a follicle, with the sebaceous glands belonging 

 to it, is isolated, particularly after the employment of acetic acid, in the form 

 of small bundles by the side and in front of the sebaceous glands, but best 



