I have elsewhere[6] endeavoured to prove, that we have a certain quantity of action present in the system at large, and properly distributed amongst the different organs, forming an equilibrium of action; and that if one organ act in an over degree, another, which is connected with it, will have its action lessened, and _vice versa_. The same holds true with regard to different actions belonging to the same organ; and the fact is of considerable importance, both in explaining and curing diseases. During pregnancy, the muscular fibres of the uterus are dormant, possessing no contractile action; at least, none qualifying them for contracting, so as to make the uterus smaller. I doubt much if even the individual fibres possess a power of alternately contracting and relaxing, as in other muscles, in any degree whatever. But, whenever the action of gestation ceases, action is communicated to these fibres; and whenever this loss on the one part, and gain upon the other, is universally begun in the womb, the transference will be completed, and the ovum can no longer be preserved in the uterus. The loss of action is generally speedy, when once begun. Perhaps in most instances it takes place instantaneously, and then the fibres begin individually to act; but they may not, for some hours, contract universally, and all at one and the same time producing pains. But if some other organ shall receive the surplus of action, or the transferred action, then the uterine fibres either will not contract, or will receive an inferior and insufficient degree of action, and expulsion will not take place until the organ sympathizing shall cease to have the increased action, whether it be the brain, the stomach, or the external muscles of the body. Sometimes also the action seems to be divided betwixt the uterus and other organs, or they alternate in their actions. This fact is of importance in explaining and correcting many of the irregularities attending labour, which it would be impossible here to specify. Sometimes the action is chiefly communicated to one part of the uterine fibres, whilst the rest are more torpid; and this part contracts in an undue degree, clasping the child firmly, and retarding labour[7]; and, after expulsion, it is apt to return, and retain the placenta, whilst the rest of the uterus becomes torpid, producing flooding. If, then, the action of gestation cease universally in the uterus, another action, namely, muscular contraction, begins, and then all hope of retaining the ovum any longer is at an end. I know that we have been told of instances where contraction, after beginning, stopped for several weeks.