Whenthe child is brought into the world by the unaided efforts of nature, and without any accident to itself or the mother, it is called aNatural Delivery. When it occurs by the efforts of nature alone, but not advantageously for both, it is not called natural, but simplySpontaneous Delivery. And when assistance is required it is called anArtificial, ordifficult Delivery. It is also calledprecocious, ortardy, according as it comes before or after the full term.
What it is that causes labor to commence, and proceed, is not fully known. At the proper time the Uterus prepares to cast out the fœtus it has so long retained, in the same manner that the tree casts off its fruit, and from some efficient cause which we have not yet discovered.
It is probable that, when the fœtus attains a certain size, it presses upon the nerves of the neck of the Uterus and irritates them, and they react again upon the muscular fibres of the Womb and cause them to contract, and so expel its contents. This is much the same action, in fact, as vomiting. When any body very repugnant to the stomach is swallowed, it irritates the nerves of that organ, and then they excite its muscular fibres, which, by forcible contractions, expel the offender.
It is possible, also, that the fœtus itself may instinctively assist in bringing about its own delivery, as was supposed of old by Hippocrates, and more lately by Harvey and others. It is certain that labor is both more difficult, and more dangerous, when the child is dead; though it may take place as usual after the death of the mother, providing the child be still alive. Several instances of this kind have been known, when the living child was expelled from the Womb, by the natural process, sometime after the mother had ceased to breathe.
The contraction of the muscular fibres of the Womb however, must be regarded as the immediate or efficient cause of fœtal expulsion, let them be brought on how they may. The muscles of the Abdomen, and the diaphragm, also assist, in the last stage, but are not essential.
The young of some of the lower animals are observed to perform certain peculiar motions, during delivery, by which it is much facilitated; and this is considered a proof, by some, that voluntary movements of the fœtus assist in the process. Certainly if it be supposed, as we have shown there is good grounds for doing, that the child assists in placing itself in the bestposition, it is equally probable that it also assists in its own expulsion, in other ways.
Premonitory Signs.—A few days before delivery the Uterus descends much lower, so that the diaphragm and stomach are less pressed upon, and the breathing and digestion becomes easier in consequence. The ease which is thus experienced is sometimes so great that the female becomes unusuallyanimated and cheerful, and cannot think she is so near her travail. This is not always the case however, for some on the contrary feel very uncomfortable and melancholy. The lips of the Vulva are also apt to swell and become painful, and the lower limbs numbed and cramped, owing to the child's head pressing on the large nerves. The neck of the bladder is also very liable to be compressed, so that a constant desire is felt to urinate, and a similar trouble may also be experienced in the Rectum. Most of these inconveniences, but particularly the numbness and cramps in the limbs, are not likely to be experienced except when the head presents, because no other part is so formed as to be able to descend sufficiently low; when they are felt therefore, the female may console herself by the reflection that they indicate, with tolerable certainty, that the child is presenting in the best position it can for a safe and speedy delivery.
Standing, or walking, usually become more difficult, and swelling of the external parts, or piles, are apt to occur. With some females also, a sudden diarrhœa, or vomiting, takes place, and troubles them up to the period when labor commences.
Finally the Uterus begins to contract, though insensibly at first; the Abdomen becomes unusually hard, and flying pains are experienced, particularly with first children. This continues with more or less of intermission, up to the actual period of labor, which is usually divided intothreeperiods, each of which must be considered separately.