Page 604 - My FlipBook

614 DENTAL EMBRYOLOGY AND HISTOLOGY. a

the cells of which, in being pushed up from the infant layer, have car-
ried a certain amount of protoplasm with them, surrounding each cell.
A marked diti'erence is seen between this protoplasm, which surrounds
the nuclei of the older layer, and that surrounding the nuclei of the
infant layer. In the latter case, with hsemotoxylon and eosin, it stains
very readily and darkly, while in the former it appears as an un-
stained mass surrounding the nucleus. The nucleus is the germinal
matter, while the unstained mass surrounding it is the formed material
(Beale). The nucleus and the formed material constitute what is com-
monly known as a cell.
These cells are surrounded by a certain quantity of protoplasm, which
stains darkly, as does the intercellular protoplasm in the infant layer,
and forms the lines which appear in the older layer in Fig. 343. The
quantity of intercellular material decreases as we proceed toward the
Fig. 342.

Porcine F.nibryo (il cm. X IM)- h. rogion of l)and t'p, epitheliiiin, infant layer;
; f/, embryonal con-
nective tissue. The space between the two layers was produced by" tearing the specimen
intentionally.
surface, and the quantity of formed material increases ; so that the cells
grow larger. This surrounding formed material of the cell-body is, in
all })robability, the uudigested or unassimilated ]>rotO])lasm from which
the germirud matter, or micleus, draws its nourishment.
As we ]iroceed iu our examination of older embryos we find the cells
losing their well-defined outlines, until they assume the appearance
seen in Fig. 272, taken from a scra])ing of the tongue in an adult
human mouth. They constitute the oldest layer, are farthest removed
from the source of mitrition, and c()rres])ond to the corneous layer of
the skin.
For a description of the epithelium of the skin I cannot do better
tiian make several quotations :
''The epithelium constitutes the superficial layer of the skin. Tn
is composed of tM'o layers of cells—
the adult tissue the epithelium