396 J. A. MYERS 
The method described by Lane-Claypon and Starling (’06) 
was used in making cleared preparations. 
Born’s method was used in making the wax reconstructions. 
For the study of the secretion in the new-born, animals were 
killed by bleeding, and fresh glands were cut with the freezing 
microtome. Others were fixed in 10 per cent formalin for an 
hour or so, after which frozen sections were cut. Frozen sec- 
tions were stained in 1 per cent osmic acid, plain scarlet red 
(prepared by adding an excess of the stain to boiling 70 or 80 
per cent alcohol) or Herxheimer’s alkaline scarlet red. Other 
glands were fixed in Flemming’s fluid, paraffin sections cut at 
5 » and stained with safranin. Still others were fixed, cut, and 
stained according to the method described by Bell (14). 
OBSERVATIONS 
New-born 
Microscopic sections show that the epidermis over each nipple 
area of the new-born female albino rat is nearly two times as 
thick as that in the skin adjacent to this area (fig. 1). Such a 
thickening renders the skin more opaque, thus preventing the 
blood in the deeper layers from giving a red appearance to the 
surface. Therefore, the nipple area appears much lighter than 
the immediately surrounding skin. 
On the surface in the central portion of the light area is a very 
slight elevation which represents the developing nipple, while 
partially surrounding the nipple is a shallow depression (fig. 1) 
which in most cases is partly filled with cornified cells. Periph- 
eral to the depression the epidermis becomes continuous as a 
much thinner layer surrounding the mammary gland area. 
Deep to the depression is the epithelial hood described in 
earlier papers (Myers, 716, ’17 a, and ’17b). In the new-born 
the free projection of the hood extends slightly further into the 
corium than in twenty-day fetuses. The outer and inner sur- 
faces of this projection are smooth and are covered with the 
stratum germinativum. The stratum corneum dips slightly 
between the two surfaces of the hood. 
