OF THE SKIN. 141 



same time, from their mutual pressure, they acquire a polygonal form 

 which may even be recognized in isolated cells. 



All the cells of the mucous layer agree, in essential points, in their 

 structure, and are nucleated vesicles distended with fluid. Their mem- 

 brane is pale, often difficult of demonstration in the smallest, frequently 

 quite distinct, always delicate, thicker in the larger ones, yet by no 

 means to be compared to that of the cells in the horny layer. The 

 contents are never quite fluid ; but also, excepting in the colored epi- 

 dermis (vide infra), never normally contain larger particles, granules or 

 fat-drops for example ; but are finely granulated, with more or less 

 clearly-defined granules, which invariably diminish in number in the 

 more external cells. The nucleus, lastly, is small in the smallest cells, 

 (0-0015-0-0025 of a line), in the large, of greater size (0-003-0-005 of 

 a line) ; globular or lenticular in the round and flattened cells; elongated 

 in the elongated cells. In the larger cells it appears obviously vesicular, 

 often with a nucleolus, and lies centrally in the midst of the contents ; 

 in the smaller it is apparently more homogeneous, without any visible 

 nucleolus, and so disposed that it is not unfrequently in contact with 

 one part or other of the cell-walls. 



[Most authors admit the existence of a special membrane between 

 the cuticle and the corium. Krause (loc. cit. p. 112) describes on the 

 upper surface of the corium a perfectly transparent, textureless, semi- 

 fluid, tough mass of 250 tn to 35(j tn f a ^ ne ^ n thickness, which he be- 

 lieves to be the cytoblastema of the epidermic cells, covered by a layer 

 of free nuclei and real cells. Henle (loc. cit. p. 1010) considers the 

 inferior layer of the cuticle as a continuous cytoblastema with inter- 

 spersed nuclei, and calls it the "intermediate skin." Such free nuclei 

 are admitted by Bruns (loc. cit. p. 358), by Gunther (loc. cit. p. 257), by 

 Hyrtl (p. 379), by Hassall (loc. cit. p. 242), and others, whilst Reichert 

 (MUller's Archiv, 1845), denies their occurrence, and also that of the 

 structureless membrane of Krause. Todd and Bowman (loc. cit. p. 413, 

 Fig. 84), regard the lower portion of the epidermis as consisting of fully- 

 developed cells (loc. cit. p. 404-411), and admit as the external border of 

 the corium a simple homogeneous and transparent membrane, " basement 

 membrane," which view Carpenter seems to share. My own observations 

 lead me to believe with Reichert, that the lowest layers of the epidermis 

 consist of fully-formed cells, as may be easily ascertained in most cases 

 by the addition of acetic acid, or diluted alkalies to fine vertical sections. 

 We are, therefore, not justified in drawing conclusions from those cases in 

 which the cells are not distinct, which, it is true, does not unfrequently 

 occur ; for even then the regularity of distance separating the nuclei, the 

 traces of cell-membranes observable as delicate striae between them, and 

 the distinct limitation of the Malpighian stratum, as it approaches the 

 corium, afford certain evidences of the existence of fully-formed cells. 

 The homogeneous membrane of Krause, and the basement membrane of 



