152 SPECIAL HISTOLOGY. 



they may be moistened with an indifferent fluid or with various 

 reagents, the most important 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 recognised in horizontal sections, passing through 

 the papillae and the deep layers of the epidermis. Its vessels 

 are to be studied in thin parts of the skin (genitalia, lips), in 

 the fresh condition, or in injected preparations with those of the 

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

 papillae, or in thin portions of the skin (prepuce, glans, eyelids, 

 conjunctiva bulbi) after the addition of acetic acid and dilute 

 solution of caustic soda, or according to Gerber and Krause's 

 method. Gerber boils the skin until it is transparent, lays it 

 a few hours in oil of turpentine until the nerves are white and 

 glistening, and then examines them in fine perpendicular sections 

 made with the double knife. According to Krause, the nerves 

 are seen very well after treating the skin with nitric acid, if 

 the right amount of action is hit upon. The elastic tissue of 

 the skin comes out well under the action of acetic acid, soda, 

 and potass. The smooth muscles may be readily isolated in 

 the tunica dartos — with more difficulty in the penis and in the 

 areola, where it needs familiarity with them, in order in all 

 cases, to recognise them with the naked eye. On the hair sacs 

 they are rendered visible microscopically, if a sac, with the 

 sebaceous glands which appertain to it, be isolated, especially 

 after the application of acetic acid, as small bundles near and 

 in front of the sebaceous glands, but best and very easily in 

 perpendicular sections of boiled skin (Henle). The examination 

 of the fat cells is especially instructive in thin persons, in whom 

 their membranes and nuclei are readily visible : in other cases 

 their membranes are readily demonstrable by the aid of ether, 

 which extracts the fat ; but the nuclei are seen with difficulty, 

 though they may occasionally be discovered here and there 

 even in full cells. The epidermis must, for its Malpighian 

 layer especially, be examiued fresh, in fine perpendicular sec- 



