the foetuses themselves within the pregnant uterus. In virgin rabbits it
is difficult to find the milk glands at all. When found the nipple is
minute and sections through it show the gland to consist of only a few
ducts a few millimetres in length. Five days after impregnation the gland
is about 2 cm. in diameter. Nine days after impregnation the glands have
grown so much that the whole inner surface of the skin of the abdomen is
covered with a thin layer of gland tissue. In six cases by injecting
subcutaneously extracts of foetus tissue Starling and Lane-Claypon
obtained a certain amount of growth of the milk glands. The hormone in the
case of the pregnant rabbit is of course acting continuously for the whole
period of pregnancy, while the artificial injection took place only once
in twenty-four hours, and the amount of hormone it contained may have been
absorbed in a very short time. The amount of growth obtained
experimentally in five weeks was less than that occurring in pregnancy in
nine days. Extracts of uterus, placenta, or ovary produced no growth,
although the ovaries used were taken from rabbits in the middle of
pregnancy. In one experiment ovaries from a pregnant rabbit were implanted
into the peritoneum of a non-pregnant rabbit, but on post-mortem
examination of the latter eleven days later the implanted ovaries were
found to be necrosed and no proliferation of milk gland had taken place.

The conclusions of Starling and Lane-Claypon were confirmed by Foa,
[Footnote: _Archivo d. Fisiologia_, v., 1909.] and by Biedl and
Koenigstein, [Footnote: _Zeitschrift f. exp. Path. und Therap_., 1910.] Foa
states that extracts of foetuses of cows produced swelling of the mammae
in a virgin rabbit.

O'Donoghue, however, concludes from a study of the Marsupial _Dasyurus_
that the stimulus which upon the milk glands proceeds from the corpora
lutea in the ovary. In this animal changes in the pouch occur in