DETERMINING CAUSES.
The earliest view attributed to the fcrtus active participation in its ex pulsion. Fatigued and irritated, either by a special acridity 'of the am niotic fluid which irritated the skin, or by an over-accumulation of me conium in the bowel, by urine in the bladder, by high temperature in the uterine cavity, by the pressure of the head on the inferior segment, by increased pressure of the uterus, by obliteration of placental vessels, by inefficient respiration, and inadequate nourishment, or by contraction of the foramen of Botalius, of the ductus venosus or of the ductus arterio sus, the fcetus was supposed to exert force upon the uterine wall, and by its efforts, to seek to escape from the uterus. All these causes are hypo thetical, for the fcetus often dies, in utero, and labor nevertheless occurs. On the contrary, when the fcetus dies, it becomes a foreign body, which the uterus endeavors to expel, and this is one of the most frequent causes of abortion and of premature delivery. The foetus, therefore, plays no active part in labor. Those rare cases in which dead women have been delivered, even of living children, may be explained, as we shall see, with out invoking the aid of the fcetus.
The determining causes were later sought for in conditions of the mother or of the ovum. It has been suggested that the ovum detached itself, at term, from the womb, as a ripe fruit from the tree, and Hulce, Naegele, but particularly Simpson, followed by Schroeder, have given the following explanation: Toward the end of pregnancy a slow but progressive fatty degeneration of the serotina takes place. This destroys the organic connection previously existing between the ovum and the uterus. At all the points where this degeneration has progressed to a certain degree, the uterine nerves are irritated. But a certain sum total of uninterrupted stimulation is necessary to call reflex uterine contrac tions into play. When this necessary stimulation is produced, reflex contractions occur. But, as the contractions grow stronger, they separate the uterus and the fcetus to a greater extent, which, by augmented irrita tion of the nerves, induces contraction sufficiently strong to finally expel the ovum. All causes producing the necessary irritation will thus deter mine uterine labor pains, as the sound, injections and diseases of the ovum. According to Simpson, degeneration of the decidua commences at the fourth month. Langhans, Dohrn, de Sinety and Leopold do not believe that the degeneration begins so early. The above explanation is not re ceived by Steinzel, who seeks the cause of labor in menstrual congestion, and attributes it to what he calls the nisus periodicus. Discomfort from catamenial congestion, however, is chiefly observed in the early months, and the irregularities of menstruation are of themselves sufficient to dis prove this hypothesis. Lobstein and Chaussier first sought the cause of labor in the complete development of the uterus. They say that labor occurs when the muscular fibres of the uterus have reached their maxi mum growth. How, then, are abortions accounted for? Loder, Mau riceau and Scanzoni admit that, at the eighth month, the uterus has reached its maximum development. After that time, the uterine cavity is enlarged by distension. This can not go beyond a certain degree, hence the occurrence of labor. Brown-Sequard, Obernier, Kehrer, hold that the irritability of the uterus, progressively increasing, reaches its maxi mum at fall term. Because of over-growth of the venous system, a con siderable quantity of venous blood is held in the uterine walls. Now, this blood is heavily charged with carbonic acid, which is one of the most powerful stimuli to muscular action. Hence a first contraction, which
expels the blood from the veins, and would thus put an end to contrac tions, if the paimit caused did not, in turn, excite the spinal cord. But, muscular action being necessarily intermittent, the fibres relax, a new afflux of blood ensues, and consequently, another contraction. Labor is the final result of the succession of these phenomena. Tyler Smith, modifying Steinzel's hypothesis, holds that true pains occur during the tenth menstrual epoch as the result of congestion, which is, thus, the de termining cause of labor. Levret, Baudelocque and Desormeaux, return ing to the theory of Lobstein and of Chaussier, hold that there is an an tagonism between the fundus and cervix as regards development. The development is accomplished at the expense of the fibres of the fundus and body during six months. Later, the cervix participates actively, and, becoming widened from above downward, is effaced. Finally, the longi tudinal fibres overpower the circular cervical fibres, dilatation follows and labor takes place. Antoine Petit goes still farther. He believes that " the cervix is a store-house in which the uterus holds in reserve the mus cular fibres, which, by their development, provide for uterine expansion during gestation. Everything is so measured, that when the fcetus is suffi ciently developed to support the influence of external agents, all the cer vical fibres have yielded, and the store is exhausted. But the child con tinues to grow, and, as he cannot do so without more space, the cavity in which he is contained is enlarged by the elongation of the uterine fibres. This elongation produces irritation, and contractions must follow, with the known results." The opinion of Antoine Petit has been negatived by the researches of Stolz, who showed in his thesis that the cervix does not change in length, during pregnancy, and that it is only effaced in the last days of gestation. This opinion was adopted, in a modified form, by Bandl, Martin and Braune. We have already considered this subject, in Wens°, and need not revert to it here. Bandl and these authors hold that the cervical canal is replaced at last by a veritable cervico-uterine canal. So soon as this canal is formed by the softening of the cervix, and by the almost complete disappearance of the internal os, the ovum is brought into immediate contact with the external os, and irritating this orifice precipitates contractions.
At this point the theory formulated in 1819 by John Power, and ad mitted by Dubois, Pajot and Depaul, should be mentioned. Depaul, ex pressing the views of these authors, compares the expulsion of the fcetns to the expulsion of the urine and faeces, saying " The first faecal matter which arrives in the rectum remains in the upper part of this portion of the bowel, producing no stimulation, no contraction and no tenesmus. But more fwcal matter is soon added to the pre-existing mass, which, being pushed onward, reaches the lower part of the rectum and is arrested by the sphincter. The faeces, in contact with the sphincter, engender, by reflex action, a desire to defecate and rectal contractions ensue. The sphincter at first resists, but its opposition being soon overcome by con tinued rectal contraction, it opens and the frees escape. Micturition oc curs in the same way. The determining cause of the expulsion of the human ovum is of the same nature." The ovum coming, at last, into contact with the uterine sphincter, excites uterine contractions, which finally produce cervical dilatation and the expulsion of the foetus.