Termanini, Kilian, Schmidt, Carus, Ritgen and Stein, regarded the point of placental insertion as the determining point in the position of the foetus.
Paul Dubois, in a series of celebrated experiments with foetuses of four to nine months, proved that the centre of gravity is not situated in the head, but at a point in the trunk near it. He returned to the theory of Ambroise Pare. " The fcetus by instinctive or voluntary determination makes certain movements, until it finds the position most favorable for its sojourn in the uterus, and for delivery." Veit, repeating Paul Dubois's experiments, arrived at a different con clusion, and together with Batthlener, Matthews Duncan and Schroeder, returned to the somersault theory.
Simpson offers the following objections to it: let. The vertical position that the theory assumes is not constant.
2d. The infant cannot be regarded as suspended from the umbilical cord, for it is too long, and too frequently twisted. The placental site at the fundus, also, is very variable. • 3d. Hydrocephalic foetuses rarely present by the head; acephalic foetuses frequently do so.
4th. In still or premature births (up to the seventh month), presenta tion of the inferior extremity is relatively frequent. He regards the muscular movements of the foetus as the cause of vertex presentation, but claims that they are purely reflex motions and not due to instinct or voli tion. The uterus, rounded up to the sixth month of pregnancy, becomes thereafter oval, with its smaller extremity directed downwards. The foetus in the same way forms an ovoid, the larger end of which, placed at the fundus, consists of the breech with the inferior extremities. In any other position it presses upon the uterine walls, which in their turn react and provoke reflex foetal movements, which persist until a vertex pre sentation is attained.
Though denied by Ritgen, Wolckler, Cazeaux, and Jacquemier accepted this theory.
Gauriet, Creff, Kristeller regard the uterine contractions occurring during pregnancy as the cause of the cephalic presentation.
Scanzoni admits all the suggested causes : the effect of specific gravity, the influence of the shape of the uterine cavity, of the form of the foetus, of the quantity of the liquor amnii, and even'the active movements of the foetus.
Cohnstein believes that the different conditions of the foetal circulation, during the first six months and after that time, will explain the relative frequency of vertex presentations. Until the sixth month, the superior half of the foetus receives more blood than the inferior half; the latter is heavy from the increased vascujar tension, and hence frequently presents. But at the seventh month an inversion occurs, so that the lungs, which are not functionating, and which are not therefore subject to their sub sequent pressure, may receive the increased blood pressure ! ! ! As we see, there are explanations enough; unfortunately there are numerous objections to each. It is to Pajot that the merit belongs of having first formulated the law of foetal accommodation, which is as follows: " When one solid body is contained in another, and if the latter is alternately in a state of motion and of repose, and if the surfaces are rounded and smooth, the included body constantly tends to accommodate its shape and dimensions to the shape and capacity of the containing body." This law, which we accept in its integrity for pregnancy as well as for delivery, is only admitted as active by Tarnier and Chantreuil during delivery. They return to the theory of Dubois and of Simpson, without deciding whether the movements are instinctive or reflex. The foetus is pressed upon by the uterine walls, they say, seeks the most convenient position, and adopts an ovoid shape to correspond to that of the uterus. The following positions may be assumed: 1. The narrow transverse diameter of the uterus hinders trunk pre sentations; hence the fcetal ovoid tends to place itself vertically, either by its own movements, or in consequence of uterine pressure.
2. At the fifth and sixth months of pregnancy the pelvic extremity, with the limbs, is no larger in volume than the head; hence either end of the fcetal ovoid may occupy the inferior segment of the uterus, and breech presentations are as common as those of the vertex.