OF THE SKIN. 



1 11 



boiling for four 



invisible. The same thing occurs after 

 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, globular vesicles, 

 without nucleus or granules, and with sharp, moderately- 

 thick contours, 0-02 — -032'" in breadth, and 0016 — 02'" 

 in thickness. If concentrated, solutions of the caustic alkalies 

 render the plates at first smaller, so that they measure only 

 0*012 — 016'", 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 col- 

 lected in the cells, into greater 

 and smaller granular masses ; 

 after the action of the heat for 

 five hours, all the cells disap- 

 pear 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 delicate 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 with- 

 stand the operation of this reagent even less than the cells; 

 whilst, when the latter are dissolved, a granular or striated sub- 

 stance remains behind, which is, probably, partly fat. Concen- 



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

 partially and wholly distended, x 350. 



Fig. 57. 



