148 SPECIAL HISTOLOGY. 



Malpighian layer becomes pale under the action of cold, concentrated 

 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 invisible. The same thing occurs 

 after boiling for four minutes. 



Caustic potass and soda act differently, according as the solutions used 

 are concentrated or diluted. In the latter case, immediately after the 

 addition of the reagent, the horny layer is rendered more clear, it swells 

 up and changes in a short time into a beautiful tissue of pellucid, glo- 

 bular vesicles, without nucleus or granules, and with sharp, moderately- 

 thick contours, 0-02--032 of a line in breadth, and 0-016-0-02 of a line 

 in thickness. If concentrated, solutions of the caustic alkalies render 

 the plates at first smaller, so that they measure only 0-012-0-016 of a 

 line, and are at the same time more wrinkled and pale, but with defined, 

 dark contours ; in the course of an hour they swell up so as to appear 

 as cells, but it takes two or three hours to give them the aspect of the 

 plates which have been heated with dilute solutions. Boiled with these 

 fluids, even the dry horny layer swells up, in an instant, into the most 

 beautiful tissue of cells, without either granules or nuclei (Fig. 57), and 

 at the same time the dissolving cell-contents mixed with the alkali, are 



collected in the cells, into greater and 

 smaller granular masses ; after the 

 action of the heat for five hours, all the 

 cells disappear without leaving a trace, 

 and yellowish and pale fat-drops in no 

 great number, swim in the liquid. The 

 cells of the Malpighian layer are still 

 more acted upon by alkalies than those 

 of the horny stratum : they swell up 

 at once, and appear distinctly as deli- 

 cate vesicles; these then dissolve, all 

 but the uppermost two or three layers, 

 which require a longer time, like those of the horny stratum, though 

 less than the latter. The nuclei of all the cells withstand the operation 

 of this reagent even less than the cells ; whilst, when the latter are dis- 

 solved, a granular or striated substance remains behind, which is, pro- 

 bably, partly fat. Concentrated sulphuric acid, in five minutes, causes 

 the horny layer to swell up so much, that its elements, although still 

 remaining flattened and irregular, appear quite distinctly to be vesicles ; 

 after half an hour they are somewhat more distended, and easily sepa- 

 rable from one another. By boiling with this acid the plates swell up 



FIG. 57. Horny plates boiled with caustic potassa and distended ; the contents partially 

 and wholly distended. Magnified 350 diameters. 



