OF THE SKIN. 157 



its cells from the liquor amnii. The smegma generally appears about 

 the sixth month, varies greatly in quantity, and is, especially in newly- 

 born infants, sometimes very greatly developed (as much as 8-J drachms, 

 Buck), sometimes wholly wanting ; in which latter case it either becomes 

 mixed with the liquor amnii, which in fact often contains epidermic 

 cells as well as fat (Mark, in Heller's " Archiv," 1845, p. 218), or may 

 have been from the first, less developed. After birth the smegma is 

 thrown off in the course of from two to three days, and the permanent 

 epidermis appears, of whose further changes up to the adult state there 

 is little to be said. In a child four months old the epidermis measured: 



Epidermis in toto. Rete Malp. Horny layer. 



On the heel, . . 0-26 of a line. O12ofaline. 0' 14 of a line. 



On the back of the foot, 0048-OOG of a line. 0002-0-04 of a line. O'OlG-0'02 of a line. 



On the palm, . . O'07-O'l " 0'04-0'07 " 0'03 " 



On the back of the fingers, 0-05G-0-07 0'04-0'05 u O'OlG-0'02 " 



On comparing this with the adult, it is to be observed that the epidermis 

 of the young child is disproportionately thick, and that this thickness 

 depends especially upon the rete Malpighii, whilst the horny layer 

 exhibits only a slight development. The pigment of the rete Malpighii 

 arises, in the colored races, only after birth. P. Camper (" Kleinere 

 Schriften," 1782, Bd. I. p. 24) saw a negro child, which at its birth was 

 reddish, and hardly differed from that of a European, rapidly become 

 tinged black at the edges of the nails and round the nipple. On the 

 third day the genitalia became colored, and on the fifth and sixth the 

 blackness spread over the whole body. In Europeans also, at birth, the 

 pigment of the areola and of the other places which have been men- 

 tioned, is not yet present: it is gradually developed in the course of the 

 first year, so that in children of two or three months old it is only indi- 

 cated. 



In investigating the skin, perpendicular and horizontal sections of 

 fresh, dried, and boiled preparations are serviceable: they may be mois- 

 tened with an indifferent fluid or with various reagents, the most impor- 

 tant points in regard to whose effects have been noticed in the foregoing 

 paragraphs. The epidermis is separated from the corium by maceration, 

 by boiling, and where it is not thick, as on the genitalia, by acetic acid 

 and soda, easily and in large flakes, so that its lower surface and the 

 papillae of the corium become visible in the most beautiful manner, and 

 the latter may be examined singly or in groups. In the fresh skin their 

 position and number are quickly and easily to be recognized in horizon- 

 tal sections, passing through the papillae and the deep layers of the 

 epidermis. Its vessels are to be studied in thin parts of the skin (geni- 

 talia, lips), in the fresh condition, or in injected preparations with those 

 of the rest of the skin ; its nerves in perpendicular sections, in isolated 



