224 
CHAS. H. o’DONOGHUE. 
both cases to the removal, by death, of the placenta. The latter 
authors, from a consideration of the results obtained by the 
removal of the internal genital organs and ovaries (cited 
above), come to the conclusion that 61 . . . lactation is due 
to the removal of the stimulus, which, during pregnancy, 
occasions the hypertrophy of the mammary glands.” Both 
Halban and Lane-Claypon and Starling regard such a stimulus 
as arising either in the placenta or the foetus. There are four 
classes of facts of which neither of the above theories is a 
sufficient explanation. Firstly, they do not account for the 
production of milk in the case of virgins nor in the interesting 
case reported by Gelhorn (loc. cit.), where milk was pro- 
duced at each menstruation. Secondly, they do not account 
for the fact that in the rabbit true milk is obtainable from 
the gland during the last two days of pregnancy, i. e. before 
the removal of either foetus or placenta. Thirdly, the 
secretion of milk in the newly born young, a subject discussed 
at some length by Bronha (loc. cit.) tells against the theory 
that the inhibitory secretion has its origin in the foetus, as in 
this case there is no removal of the stimulus and yet there is 
milk produced. Lastly, they do not account for the large 
growth of the mammary gland, identical with that taking 
place in pregnancy, and probably followed by a small secre- 
tion of milk, which occurs normally in Dasyurus when ovula- 
tion is not followed by fertilisation. 
Up to the present, then, there does not appear to be a 
satisfactory explanation of the causation of milk secretion, 
and the view that it is due to the removal of an inhibitory 
stimulus whose origin is the placenta or foetus, consequent 
upon parturition, must be regarded as by no means fully 
established. 
General Summary. 
Formation of the Gland. — (1) The teat anlagen arise 
from a proliferation of the cells of the Malpighian layer of 
the epidermis. 
