426 J. A. MYERS 
study lead to the conclusion that in the rabbit, cat, bat, and 
white rat the so-called new-born secretion does not contain fat 
and hence is not a true lactation as is found in human. This 
failure to produce true milk in some of the lower forms may be 
due to the feeble development of the mammary gland in the 
new-born. The lumina are not completely formed at birth in 
the rat, cat, and rabbit, therefore the cells may be unable to 
produce a true milk secretion when the stimulus is received. 
On the other hand, Brouha found the lumina quite well repre- 
sented in Vespertilio murinus at the time of birth. The question 
then arises as to whether the stimulus which produces a true 
lactation in the human new-born is actually present in the lower 
forms of animals. Further experimental evidence is necessary 
to decide this question. 
Gland stroma 
Attention was called to the fact that the stroma in the fetus 
is divisible into the mantle layer closely surrounding the ducts 
and the true stroma between the ducts. This arrangement of 
the stroma persists through the ten weeks’ stage. The mantle 
layer increases somewhat in thickness as age advances. ‘This 
layer diminishes in thickness as one passes from the primary to 
the terminal ducts. About the third week of postnatal life a few 
elastic fibres appear in the mantle layer surrounding the primary 
and secondary ducts. In later stages elastic fibers are more 
numerous and extend further toward the free end of a system of 
ducts. The true stroma is at first composed of loose connective 
tissue, but soon after birth there appears such a tremendous 
invasion of fat that the mantle layer of the ducts is almost en- 
tirely surrounded by fat cells. 
Free red corpuscles were observed in the stroma twelve hours 
after birth, but were not seen in any of the later stages. White 
blood-cells were observed in the true stroma in all stages studied, 
but in no stage did they appear in greater numbers than they 
are usually found in the neighboring tissues. 
Berka (’11) called attention to the presence of elastic fibers 
in the mantle layer of the virgin human ducts. Schil (12) 
