On the Development and Growth of the Epidermis. 83 



menced, is next to impossible; and in the living state of the 

 body, separation never takes place until the mutual connexion 

 between the layers has been destroyed by the effusion of fluid. 

 The microscope gives additional weight to this evidence. I 

 have observed that the cells of the deep surface of the epider- 

 mis are in immediate contact with the boundary limit of the 

 dermis, and that moreover it is frequently difficult to deter- 

 mine the exact line between them. I have also made the fol- 

 lowing experiment : — I cut very thin vertical slices of the skin, 

 at daily periods, from the moment of death until decomposition 

 had become established, and submitted them to the action of 

 the compressor on the field of the microscope, but in every 

 instance, while fresh, the two tissues yielded to the pressure 

 in equal proportion without any separation occurring. As 

 soon, however, as decomposition had commenced, separation 

 was produced, and in the early stages took place with diffi- 

 culty. This experiment proves that the firm adhesion sub- 

 sisting between the epidermis and dermis is not alone due to 

 the numerous inflexions of the former into the latter, which 

 take place at the sudoriferous tubes, hair, tubes, and sebaceous 

 ducts, although these inflexions must co-operate powerfully in 

 the result. 



Being desirous of examining the under surface of the epi- 

 dermis with the higher powers of the microscope, and failing 

 in all my attempts to effect this object by taking the entire 

 thickness of the epidermis or scraping, I awaited the first in- 

 dication of its separation from the dermis, and then removing 

 it carefully made a thin slice parallel with the surface which I 

 wished to examine. This plan succeeded beyond my expec- 

 tations ; for not only did I obtain parts so diaphanous as to 

 enable me to see the surface distinctly, but the septa between 

 the depressions for the papillae of the dermis afforded natural 

 laminae of such transparency as permitted their structure to 

 be well examined. 



When the under surface of the epidermis was exposed to 

 view, I found it to be composed of four kinds of elements, ar- 

 ranged in such a manner as to constitute an irregular mosaic 

 plane. These elements are, — 1, granules, measuring about 

 2^ n ytli of an inch in diameter; 2, aggregated granules, mea- 

 suring about y^^th ; 3, nucleated granules, measuring ^^th 



to ^ouo 1 ' 1 ' 4 > ce ^ s » measuring rGTTB& to 2joo tn °^ an mch. 



1. The granules, which I may distinguish by the name of 

 primitive granules, are globular in form, homogeneous, solid, 

 brightly illumined by transmitted light when the centre is 

 under the focus of the microscope, but dark when viewed upon 

 the surface, the darkness being increased whenever they are 



