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When pregnancy does not occur the corpus luteum is formed, but begins to diminish within ten or twelve days in the human species and is then gradually absorbed. According to O'Donoghue, in the Marsupial Dasyurus there seems to be no difference either in the development of the milk glands or of the corpora lutea between the pregnant and the non-pregnant animal. Lin.
Thus "butter and eggs" and "eggs and bacon" are applied to several plants, from the two shades of yellow in the flower, and butter-churn to the Nuphar luteum, from the shape of the fruit. A popular term for Nepeta glechoma is "hen and chickens," and "cocks and hens" for the Plantago lanceolata.
On this view that the corpora lutea are the result, not the cause, of intra-uterine gestation, it would no longer be possible to maintain the theory that the corpus luteum in the human species is the cause by its internal secretion of the phenomenon of menstruation. Leopold and Ravana found that ovulation as a rule coincides with menstruation, but may take place at any time.
Possibly the corpus luteum, the endocrine formed of the torn egg nest in the ovary, makes up for any deficiency in this respect. For there is the most curious resemblance imaginable between the cells of the adrenal cortex and those of the corpus luteum, some day to be completely explained.
Their atrophy at the menopause coincides with the shrinkage of the ovaries that takes place at that period. Activity of the breasts parallels indeed more or less the activity of the corpus luteum. With the prolonged activity of the corpus luteum during pregnancy, prolonged stimulation of the breasts occurs.
What seems to happen in fact, is this: the corpus luteum secretion stimulates the dormant cells of the mammary glands, formed during puberty, but latent until the advent of pregnancy. We know that injection of corpus luteum will cause an hypertrophy of the breasts. The same effect is produced regularly during the menstrual period, with a consciousness of swelling of the breasts.
What concerns us now is its internal secretion or secretions. One of them is known as lutein and it has never been chemically isolated in its pure form. The existence of lutein, like the existence of electricity, is an inference, something we are sure is there because of its effects. It originates in a remarkable part of the ovary, the corpus luteum.
If death occurred immediately after delivery, the uterus will be wide open, about 9 or 10 inches long, with clots of blood inside, and the inner surface lined by decidua. The difference between the virgin corpus luteum and that of recent pregnancy is not so marked as to justify a confident use of it for medico-legal purposes.
The true corpora lutea arise from follicles in which the ova have become mature and from which they have escaped through the surface of the ovary. Buds from the theca interna invade the follicle and form the connective tissue of the corpus luteum.
If pregnancy and the consequent placenta do not occur, it shrinks and turns into a scar, the false corpus luteum. The true corpus luteum resembles closely the adrenal cortex in make-up and staining reactions.
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