On the causes responsible for the developmental progress of the mammary glands in the rabbit during the latter part of pregnancy
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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. 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.