STUDIES ON THE MAMMARY GLAND 427 
observed elastic fibers in rabbits six months of age and at the 
age of puberty. 
Red blood corpuscles were observed in the true stroma of the 
glands of premature and mature infants by Schlachta (’04). 
Brouha (’05) found capillary hemorrhage exists in the stroma of 
all infants that died from abrupt asphyxia. He noticed, how- 
ever, that in infants dying from other causes there may be a 
considerable extravasation of red blood corpuscles. Both of 
these authors concluded that the red corpuscles probably reached 
the stroma through the process of diapedesis. Owing to the 
presence of red blood-cells in the mammary-gland stroma of the 
albino rat in comparatively small numbers, it is possible that 
they reach the stroma through the process of diapedesis. How- 
ever, it must be borne in mind that during parturition and the 
removal of the skin there is considerable danger of trauma. 
Several authors have reported the presence of an abnormally 
large number of leucocytes in the true stroma of the mammary 
gland at or soon after birth. Czerny (’90) believed they play 
an important réle by entering the lumina of the ducts and carry- 
ing the secretion into the lymphatics. Schlachta (04) was un- 
able to confirm Czerny’s finding. Brouha (’05), however, found 
the immigration of leucocytes in the gland stroma to be less 
marked during the activity of the new-born gland than before 
or after such activity. The fact that the secretion in the albino 
rat is very slight and never becomes a true milk secretion proba- 
bly accounts for the absence of an infiltration of leucocytes. 
SUMMARY 
The results of the present study on the mammary gland of 
the male and female albino rat from birth to ten weeks of age 
may be summarized briefly as follows: 
1. Owing to the thickening of the epidermis over the develop- 
ing nipple of the new-born female albino rat, the mammary- 
gland area appears lighter than the surrounding epidermis. In 
the male no epidermal thickening is present, hence the mammary- 
gland area is not visible. 
