Retractility and contractility, however, would not suffice to cause dimi nution in size of the uterus, if to these factors were not added the process of fatty degeneration which invades each anatomical element, and which causes the disappearance of certain of these elements, and their reproduc tion by new elements, and further causes diminution in size, acquired during pregnancy, of other elements; in a word, the process which sub stitutes normal conditions for the hypertrophic of gravidity. In one case, there is total destruction of old elements, and entire new formation; for others, there is not total destruction, but simple resorption of a part, and return to the normal, without new development. the theory of new formation of muscular fibre has been championed by Kolliker, Heschl, Virchow, Aran and Sappey, while Robin, denying hypergenesis of uterine elements during pregnancy, and recognizing only their hypertrophy, denies total elemental destruction during involution.
Heschl maintains that the modifications invade all the anatomical ele ments, the peritoneum, the muscular tissue, the mucous membrane, the arteries and nerves, that the muscular tissue is entirely laid bare through the shedding of the decidua, except at the point of placental insertion and in the cervix, the mucous membrane of which, usually, remains intact with its hypertrophied papillte, and its glands. Heschl, hence, is opposed in his views to Kilian, Robin, Arnold, Virchow, Duncan, Rolleston, Fried lander, Langhaus, and Leopold, who contend that the muscular coat is never laid bare, and that there always remains a portion of the old mucous membrane, which gives birth to the new mucous membrane through cell proliferation.
It is in the muscular tissue, and in the mucous membrane of the uterus, that the greatest changes occur. The substance of the uterus undergoes such a complete transformation into fat, that, according to Heschl, there does not remain a single one of the original cellular fibres of the uterus. Jenks is of the same opinion. This transformation begins about the fourth day, sometimes not until the sixth, never later than the eighth, and it extends regularly throughout the body, the cervix not partaking till later. Soon it is found that the degeneration is more marked in the internal than in the external layer. It begins in each of the muscular fibrils at many points together. Them fibres lose their tortuous form, the borders become pale, and we perceive faint patches, which, since the ex tremities of the fibrils are thin, quickly isolate the fibrils. These patches
remain apparent until masked by the globules of fat, which are constantly multiplying. Rapid absorption of this modified tissue now takes place, and this absorption is manifested by the diminution in size of the organs. As a result of this fatty degeneration, the uterus becomes more friable, and this persists until the return to the normal. The organ loses its red color, it assumes a reddish-yellow. At the fourth week, the first ele ments of the new uterine substance appear as follows: In the external layer appear cells, then fibrillar elements, which take on the shape of muscular fibres, and which are the new uterine substance. While the muscular substance of the organ is undergoing destruction, and becoming absorbed, the new tissue is everywhere developing, so that at the end of the second month, usually, the renovation is completed. The veins and the capillaries undergo a similar fatty degeneration. The point of pla cental insertion changes more slowly. Normally the veins are filled with thick clots, and project above the muscular tissue, between the muscular bundles which are undergoing degeneration; so that, at the end of the fourth or the sixth week, the point of placental insertion is still recogni zable by the jutting out of the uterine tissue in this locality. Finally, the clots disappear, the veins become indistinct, the level is re-established, and the new mucous membrane covering all, the site of the disappears, and is no longer recognizable. Nevertheless, for many months, there is a slight elevation at this site.
As for the mucous membrane, a few days after delivery this is carpeted by a reddish, soft, pulpy, floating substance. If the mucous membrane of the cervix be not affected, this substance is sharply outlined at the level of the internal os, spreads over the entire surface of the body, in thick ness like a sheet of paper. Under the microscope, this substance is made up of pavement and cylindrical epithelial cells, and, in the layers nearest the new muscular coat, it consists of new fibrous tissue (tissue conjunc tif). At the end of the third week the vessels reappear, sometimes even later. Until then the blood is apparently contained in trenches formed by the cells lying close together. The glands are renewed at the end of the second month. Heschl has not been able to follow their formation.