OF THE SKIN. 149 



even in a minute, without exhibiting nuclei, and in two minutes they dis- 

 appear without leaving any trace. Boiling in dilute sulphuric acid ren- 

 ders the horny layer hard and transparent, and dissolves it wholly in 4-5 

 hours. The cells of the stratum Malpighii* are little altered by cold 

 sulphuric acid : on boiling, their contours and nuclei at first become more 

 distinct, but in about two minutes the whole is dissolved. Nitric acid colors 

 the epidermis yellow, softens and changes it into xantho-proteic acid. 

 The cells of the horny layers swell up somewhat, after a time, in the cold, 

 and become granular ; the stratum Malpighii is rendered granular and 

 indistinct, and sharply defined from the horny layer. Upon boiling, the 

 whole epidermis is entirely dissolved in half a minute. Hydrochloric 

 acid does not tinge the epidermis, and in the cold renders the cells of 



* [I have recently investigated the reaction of the pigmental cells in the Malpighian 

 layer of the Negro, and with the following results. Macerated in water they remain 

 unchanged. Caustic potassa renders the outline of the cell more distinct, but produces no 

 effect on the enclosed pigment. After acting for three or four hours it dissolves the cell, 

 and allows the dark pigment granules to escape. Boiled for ten minutes in a solution 

 of caustic potassa, the cells become larger and more distinct; in many, nuclei and dark 

 granules are visible ; and their color becomes changed to a yellowish brown. Prolonged 

 boiling dissolves the cells, but does not act on the granular pigment ; caustic soda brings the 

 pigment cells distinctly into view and causes them to swell up. Continued action for one 

 or two hours, dissolves the cell and permits the unchanged black pigment to escape. Upon 

 boiling for about four minutes in caustic soda, rupture of the cell-wall with escape of the 

 contents ensues. 



Concentrated sulphuric acid has no effect on the Malpighian layer. When first added the 

 cells are rendered more distinct ; after twenty-four hours no further effect is observable. 

 Boiling in sulphuric acid produces no change on the cells; after a few minutes the whole 

 epidermis is dissolved. Nitric acid when first added had no decided action ; but after a few 

 hours it rendered the cells more indistinct, dissolving some, and staining the intermediate 

 tissue yellow. Soaked for twenty-four hours in nitric acid, the whole pigmentary layer 

 assumes a yellow color; the separate cells are scarcely recognizable. The rapidity with 

 which the whole epidermis when boiled in nitric acid is dissolved, makes it difficult to 

 determine its effect upon the Malpighian layer. 



Hydrochloric acid does not act as powerfully as nitric acid. At first its addition produces 

 no effect on the cells; in the course of a few hours, they become more indistinct, but are not 

 dissolved. The same result is obtained by allowing this acid to act for twenty-four hours. 

 The cells are then indistinct, but of a black color; boiled for two minutes they swell up, 

 enlarge, but are not rendered more distinct. More prolonged boiling (four or five minutes) 

 dissolves the whole epidermis. Acetic acid causes the pigment-cells to be more easily dis- 

 tinguished. In a preparation that had been placed for five weeks in concentrated acetic 

 acid, the cells were very distinct; but not otherwise altered. No effect was produced upon 

 the pigment. 



The action of Nitrate of silver, as it stains the horny tissue, cannot be well ascertained. In 

 a preparation, that had been placed in a concentrated solution for twenty-four hours, the 

 pigment cells, as far as they could be studied, were of a more intense color, but not otherwise 

 altered. In alcohol and ether the epidermis is hardened and the pigment-cells of the 

 Malpighian layer are well and distinctly seen, but these reagents exert no action on them. 

 Boiled in ether the cells become distinct and of a lighter color. A solution of Iodine, colors 

 the whole epidermis immediately, and thus prevents the study of its special action upon 

 the pigmental cells of the Malpighian layer. DaC.] 



