212 
CHAS. H. o’dONOGHUE. 
before parturition, and perhaps corresponds most nearly to 
those in which milk is being secreted (fig. 6). Both the 
above cases (Nos. 29 and 30), present another point of 
similarity with the stages after parturition in that no sign of 
a multiplication of the glandular cells, either mitotically or 
amitotically, was to be discovered. 
The entire series of growth-changes just described is 
identical with that which occurs in normally pregnant animals. 
It would therefore appear that although there was no 
pregnancy, the growth and activity of the mammary glands 
and neighbouring glands of the pouch area had reached a 
stage of development indistinguishable from that which 
occurs in auimals a day or two after parturition. There is 
also present in these cases a secretion which appears to be 
milk although it is not so plentiful as after pregnancy. 
These facts are of great interest in the consideration of the 
source of the stimulus which brings about the hypertrophy 
of the mammary glands during pregnancy. 
The Stimulus inciting G-rowth in the Mammary Glands. 
The Nature of the Stimulus. 
It is well known that there is an intimate connection 
between the enlargement of the uterus and the growth of 
the mammary glands during pregnancy. It would appear 
that this correlation is due to the production of a hormone 
affecting both parts simultaneously, which is carried by the 
blood, although the seat of origin of such an internal 
secretion is still the subject of much discussion. The earlier 
idea that the growth of these glands was due to a stimulus 
conveyed by the nervous connections between mammary 
glands and uterus, although maintained as recently as 1903 
by Basch 1 ( 3 ), appears to be quite ruled out by recent 
experiments. Eckhard ( 13 ) cut all the nerves supplying the 
mammary gland in the goat without interfering with lactation 
1 This work contains a very full bibliography relating to the physio- 
logical aspect of the subject. 
