534 



On the Causes Responsible for the Developmental Progress of the 

 Mammary Glands in the Rabbit during the Latter Part of 

 Pregnancy. 



By J. Hammond, M.A., Captain, Norfolk Eegiment. 

 (Communicated by J. Barcroft, F.R.S. Beceived November 9, 1916.) 



[Plate 23.] 



to 



The parts played by the various reproductive organs in causing the growth 

 of the mammary gland and the secretion of milk have been the subject 

 of much recent investigation. Most of the work has been done with the 

 •rabbit, and the changes which occur in its mammary glands have been studied 

 very minutely.* 



The causes of the growth changes in the gland during the first part of 

 pregnancy are now conclusively shown to be due to the influence of the 

 corpus luteum.f These changes in the rabbit culminate at about the 

 16th day after coitus ; after this time in pseudo-pregnant rabbits {i.e., rabbits 

 which have had coitus and developed corpora lutea, but have not become 

 pregnant) the gland undergoes atrophy. If the growth changes of the 

 mammary glands of a series of pregnant and pseudo-pregnant rabbits be 

 compared, it will be seen that the changes are similar until about the 

 16th day, at which period in the pseudo-pregnant condition the gland begins 

 to atrophy, while in the pregnant animal the gland becomes much thicker, 

 increasing rapidly in weight from the 24th to the 30th day. 



The object of the investigations described in the present paper was to 

 determine the causes of this further development of the mammary gland 

 (called by Ancel and Bouinj the glandular phase) which takes place after the 

 16th day of pregnancy. 



In the present paper it is shown that, contrary to the commonly accepted 

 ^opinion, the corpus luteum in the rabbit does not become atrophied during 

 the latter part of pregnancy, but maintains its size till late in gestation 

 and even into the period of lactation, the cause of this development 

 originating in the foetus. It is also shown that the changes in the mammary 

 gland in the second half of pregnancy are correlated with the further 

 development of the corpora lutea, and consequently that the origin of the 



* Schil, 'Becherches sur la Glande Mammaire,' Nancy, 1912. 



t Ancel and Bouin, ' Compt. rend. Soc. Biol.,' vol. 66 (1909). For further references 

 see Hammond and Marshall, 'Boy. Soc. Proc.,' B, vol. 87 (1914). 



% Ancel and Bouin, ' Journ. de Phys. et de Path, generale,' vol. 13 (1911). 



