BIRTH, or LABOR, in physiology, is the act by which a female of the class Mammalia brings one of her own species into the world. When the foetus has remained its due time in the womb, and is in a condition to carry on a separate existence, it is extruded from its i place of confinement, in order to live the life which belongs to its species independently of the mother. The womb having reached its maximum of growth with the increasing size of the foetus, its peculiar irritability excites in it the power of contraction; it thereby narrows the space within and pushes out the mature foetus. The period of gestation is very differ ent in different animals, but in each particular species it is fixed with much precision. In the womb the corporeal frame of man com mences existence as an embryo; after further development, appears as a foetus; then as an immature, and finally a mature, child. With its growth and increasing size the membranes which envelop it enlarge, the womb also ex panding to give moth for it. At the end of the 39th or the beginning of the 40th week the child has reached its perfect state and is capable of living separate from the mother; hence follows in course its separation from her, that is, the birth.
Contractions of the womb gradually come on, which are called, from the painful sensa tions accompanying them, labor-pains. These are of two lands: first, the preliminary pangs, which begin the labor, do not last long, are not violent and produce the feeling of a dis agreeable straining or pressure. When the pregnant female is involved in these she is often unable to move from her place till the pang is over, after which she is often free from pain for some hours. Then follow the true labor-pains; these always last longer, return sooner and are more violent. The contractions of the womb take place in the same order as the enlargement had previously done, the upper part of it first contracting, while the mouth of the womb enlarges and grows thin, and the vagina becomes loose and distensible. By this means the foetus, as the space within the womb is gradually narrowed, descends with a turning motion toward the opening; the fluid contained in the membranes enveloping the foetus, as the part making the greatest resistance, is forced out, and forms a bladder, which contributes much to the gradual enlargement of the open ing of the womb. It is therefore injurious to
delivery if hasty or ignorant midwives break the membranes too soon. By repeated and violent throes the membranes at length burst and discharge their contents, and some time after the head of the child appears. As the skull-bones have not yet acquired their perfect form and substance, but are attached at the crown of the head only by a strong membrane, and may be brought nearer together, the head, by the pressure which it undergoes, may be somewhat diminished in size and squeezed into a more oblong form, so as to pass through the opening of the matrix and the pelvis in which it is contained, and, finally, through the exter nal parts of generation; and when this is done, the rest of the body soon follows.
The act of birth or delivery is accordingly, in general, not an unnatural, dangerous and diseased state of the system, as many timid women imagine. It is a natural process of development, which is no more a disease than the cutting of the teeth or the coming on of puberty, although, like them, it may give rise to important changes in the body and to various diseases. It is true that the process of child birth requires a violent exertion of nature, but this is facilitated by many preparatives and helps adapted to the purpose. If the birth suc ceeds in the way described, it is called a natural birth. For this it is requisite that the pelvis should be properly formed and the open ing should permit a free passage to the per fect foetus; that the growth and size of the foetus should be proportioned to the pelvis, especially that the head should have the size designed by nature, proportioned to the diameter of the pelvis; also, that there should be a proper situation of the womb, in regard to the axis of the pelvis, and a proper position of the foetus, namely, the head down, the back of the head in front and toward the opening of the womb, so as to appear first at birth; and, finally, that the external parts of generation should be in a natural state.