150 SPECIAL HISTOLOGY. 



During embryonic life a desquamation of the epidermis 

 occurs, which is perhaps repeated several times. Such is the 

 fate, probably, of the layer of polygonal cells which arises first of 

 all, and which in the second to the fourth months, becomes 

 metamorphosed into an almost structureless membrane, and 

 is then no longer to be found ; perhaps also of the layer of epi- 

 dermis, which covers the points of the hairs which have not yet 

 appeared externally {vide infra § Hairs); and in the second half 

 of the foetal period it may be easily demonstrated as an actively 

 occurring process. From the fifth month onwards, in fact, con- 

 tinually increasing desquamation of the external epidermic cells 

 takes place, and these becoming in most parts mixed up 

 with the sebaceous secretion of the skin, form the so-called 

 vernix caseosa or smegma embryonum. This is a whitish or 

 yellowish, viscid, inodorous material, which, especially from the 

 sixth month onwards, covers the whole surface of the foetus 

 with an often considerably thick and even laminated sub- 

 stance, which is most abundant upon the genitalia, on the 

 flexor side of the joints (axilla, knee, nates), on the sole, the 

 palm, the back, the ear, and on the head in large quantity, and 

 when microscopically examined consists mainly of epidermic 

 cells, but also contains sebaceous cells and fat globules. Ac- 

 cording to Davy ( f Lond. Med. Gaz./ March, 1844) the vernix 

 caseosa contains in 100 parts, 5*75 elain, 3T3 margarin (8-88 

 fat); the rest, 911 2 per cent., must be reckoned as epidermic 

 scales, for since the vernix caseosa contains no free fluid, the 

 77*87 per cent, water and 13-25 solid substance found by Davy 

 must be laid to the account of epidermic cells. This also holds 

 good of Buek's analysis ('De Yernice caseosa/ Halis, 1844) 

 who found in 100 parts, 10-15 fat, 5-40 epithelium, and 84-45 

 water (so that there was 89-85 of epithelium); and also in two 

 other cases, in which the water was not exactly determined, he 

 found 14'80 and 9"31 per cent, of fat, and therefore 86 20 to 

 89-G9 of moist epithelium. According to Buek, the fat of 

 the vernix caseosa, contains no cholesterin, as had been stated 

 by Fromherz and Gugert, but oleic acid, and either stearic or 

 margaric acid, which are probably not free, but combined 

 with glycerine, — a circumstance which also evidences its origin 

 from the sebaceous glands, in which, normally, no cholesterin 

 is formed. Lehmann found (1. c.) in the dry vernix caseosa of a 



