140 SPECIAL HISTOLOGY. 



total analysis of the epidermis^ with regard to its two layers which 

 differ so widely; and the organic combinations, also, which 

 occur in it, are not sufficiently known. 



The so-called horn, which forms the membranes of the 

 horny-plates, is insoluble in water, easily soluble in concentrated 

 alkalies and concentrated sulphuric acid, whence the skin, if 

 wetted with these substances, feels slippery and greasy; there 

 remains, however, a small residue insoluble in alkalies; con- 

 centrated acetic acid, also, dissolves it, first rendering it 

 gelatinous, by which it is distinguished from the protein 

 compound of the hair. It contains less sulphur than the hair 

 and nails, which is perhaps the reason why salts of lead, 

 mercury, and bismuth, colour the hair but not the epidermis. 

 Besides these, Mulder finds in the horny layer a gelatinous 

 matter, which is obtained by long boiling in water, and which 

 would appear to be of a collagenous nature. The epidermis 

 does not putrefy — it melts in the fire without bending or 

 swelling up, and burns with a clear flame. 



[The behaviour of the epidermis towards reagents is 

 particularly of importance for the microscopist, on whose 

 behoof I add the following account. 



After long maceration in water, the epidermis becomes 

 detached in portions, and under moderate pressure is resolved 

 into a white powder, consisting of the isolated horny plates, 

 and the uppermost cells of the rete Malpighii. Boiled in 

 water, pieces of the horny layer break up into their 

 elements much more readily. Boiled in concentrated acetic 

 acid for 15 to 25 minutes, all the horny plates become 

 perfectly isolated, forming a cloudy, whitish deposit in the 

 test tube ; they are exceedingly pale, so that they are often 

 hardly visible under a full illumination ; and are completely 

 swollen up and changed into globular or elongated, distended, 

 but always more or less flattened vesicles of 0-0.2 — - 032'" 

 breadth, and 0'006 — 001 " thickness, the nuclei when they 

 are present being also pale and hardly to be perceived. The 

 Malpighian layer becomes pale under the action of cold, con- 

 centrated acetic acid, the cells and nuclei being rendered more 

 distinct. The cell-contents are partially dissolved : by Longer 

 action the contours of the deepest layers of cells become 



