508 Dr. J. E. Lane-Claypon and Prof. E. H. Starling. [Feb. 12, 



Observations on Man show that the secretion of true milk cannot be due to 

 a stimulus received by the gland at the time of conception, since the secretion 

 occurs whenever pregnancy comes to an end, whether at the third month or 

 at the ninth. A good account of the clinical evidence bearing on this point 

 has been given by Halban.* This observer points out that when premature 

 death of the foetus occurs without its expulsion, as in cases of extra-uterine 

 foetation, the breasts swell two or three days after the death may be presumed 

 to have taken place, and a true secretion of milk may be obtained. 



The same thing occurs when the death of the foetus happens in utero, but 

 the result is not invariable. Thus Halban mentions certain cases in which 

 the secretion of milk began two or three days after the presumed death of 

 the child, but he also gives details of other cases in which the secretion 

 occurred only after the expulsion of the dead foetus. Halban is inclined to 

 ascribe the difference between these two classes of cases to differences in the 

 placentas, and imagines that the appearance of milk in the breasts is deter- 

 mined, not by the removal or the death of the living foetus, but by the 

 removal or death of the placenta. 



The hypothesis that some special stimulating substance is formed in the 

 involuting uterus or in the ovaries after parturition seems to be negatived by 

 certain cases in which Porro's operation was performed without interfering 

 with the subsequent onset of lactation. In order, however, to decide this 

 point we have carried out a number of observations on pregnant rabbits. 

 In these the whole uterus, uterine appendages, and ovaries, were removed at 

 different stages of pregnancy. In the rabbit pregnancy lasts, on the average, 

 28 to 30 days. If in a primiparous rabbit Porro's operation be performed 

 at the 10th day or at any day before the 14th, the development of the 

 mammary gland at once ceases and gives place to retrogression. No milk, 

 however, appears in the gland, and at the end of a couple of months the 

 gland is little removed from that of a virgin animal. If, on the other hand, 

 the operation be carried out on animals after the 14th day of pregnancy, 

 within two days after the operation milk can be expressed from the nipples, 

 showing that here, as in Man, the effective factor in determining the process 

 of lactation is not the absorption of substances from ovaries or involuting 

 uterus, but the removal of certain stimuli which normally proceed from the 

 organs or foetus of the pregnant animal. 



The most obvious explanation of these results is that lactation is due to the 

 removal of the stimulus which during pregnancy occasions the hypertrophy 

 of the mammary gland. Hildebrandtf has suggested that during pregnancy 



* ' Archiv f. Gynakol.,' vol. 72, Heft 2, 1905. 

 t ' Hofmeister's Beitrage,' vol. 5, p. 413, 1 904. 



