_Twins._ If there be twins, the placenta of the first child is seldom expelled until after the birth of the second child. The membranes of the second ovum become distended with liquor amnii, project into the vagina and burst as in a common single labour; the passages have been sufficiently dilated and prepared by the birth of the first child, so that, when the uterus begins to contract, the expulsion of the second will be readily and easily effected. The uterus may resume its efforts for this purpose in twenty minutes after the birth of the first child, or it may remain quiescent for several hours without at all disturbing the regular and natural course of the process which will be precisely the same as in the previous case. The placentæ of twins are usually expelled together, forming one large placentary mass; their vessels, however, are distinct from each other, so that with care one placenta can be peeled away from the other. In other cases, they are separated from each other by an intervening space of membranes; and in one rare instance of triplet placentæ the umbilical arteries of two placentæ anastomosed with each other, before dividing into smaller branches. Upon the expulsion of the placenta, the uterus, being now emptied of its contents, contracts into a firm hard ball, which may be felt behind the symphysis pubes, or sometimes a little to one side, of about the size of a full grown foetal head. This state of hard contraction gradually disappears, and a discharge of blood called lochia follows, which having continued for a few days becomes colourless, and at length ceases altogether. For a description of the changes which the uterus and passages undergo in returning to their former condition as in the unimpregnated state, we refer to the chapter on the FEMALE ORGANS OF GENERATION. CHAPTER II. TREATMENT OF NATURAL LABOUR. _State of the bowels.--Form and size of the uterus.--True and spurious pains.--Treatment of spurious pains.--Management of the first stage.-- Examination.--Position of patient during labour.--Prognosis as to the duration of labour.--Diet during labour.--Supporting the perineum.-- Treatment of perineal laceration.--Cord round the child's neck.--Birth of the child, and ligature of the cord.--Importance of ascertaining that the uterus is contracted after labour.--Management of the placenta.--Twins.--Treatment after labour.--Lactation.--Milk-fever and abscess.--Excoriated nipples.--Diet during lactation.--Management of lochia.--After-pains._