Finally, it is possible that in man and the mammalia some such remarkable property may be possessed by the spermatozoa as that which I have observed in certain annellides. If a portion of the contents of the testis of the com mon earth-worm (Lumbrieus agricola, Hoffm.) be placed under the microscope between two slips of glass, in about ten minutes the whole mass is seen to heave and writhe with aston ishing energy, the form of the movement being that of the peristaltic action of the intestines (fig. 459.). Everything in contact with the spermatozoa becomes ciliated by them, one end of the filament fixing itself while the other vibrates free. The result is, that if the body to which the spermatozoa attach themselves is fixed, such as the glass, or the margin of a mass of granules, a line of cilia is formed whose action creates a strong current, and everything movable is drawn into the vortex, and is seen drifting rapidly along. But if the body to which they attach themselves is movable, then this soon becomes clothed with spermatozoa, m hose f'ree ends moving rapidly, cause the whole to rotate. A most remarkable object is thus formed, which continues for a con siderable time in motion, clearing for itself a free area, and in this it revolves, whilst its revolutions are apparently assisted by the ac tion of other spermatozoa, which, having at tached themselves to the periphery of the cleared space, keep up a perpetual vortex, in which the central body is partly a passive and partly an active agent.* Whether any similar effect is capable of be ing produced by the spermatozoa in the human subject, or how far this property may be ge neral in spermatozoa, I am not aware ; but the circumstance is altogether too remarkable to be passed over without mention here, as it may serve to explain how the onward move ment of spermatozoa can, in some cases at least, be aided by this peculiar property of the spermatic filaments to attach themselves to surfaces with which they were in contact, and to clothe these surfaces with a fringe of cilia capable of producing the ordinary effects of cilia in motion.
The office of the uterus in gestation.—The process of gestation may be considered to commence from the moment that the ovum, which has been subjected to the fertilising in fluence of the male generative element in the Fallopian tubet, is received impregnated into the uterine cavity. If no such contact of the generative elements as is necessary to the de velopment of the ovum takes place, then the latter suffers no further change beyond that slight alteration in its condition during its passage through the oviduct, which has been already described ; and ultimately it becotnes lost, probably suffering decomposition, but at least giving no evidence of its presence in the uterine cavity. But if the ovum has been fer tilised, then commences that remarkable series of changes in the physical condition of the uterus whereby this organ is fitted for the pro tection and nutrition of the ovum during the usual period of forty weeks in which the latter is normally retained within its cavity. As these changes involve very considerable alterations in the form and composition of the entire uterus, as well as of its several parts, they have been considered as a part of that series of meta morphoses which the uterus undergoes in its progress from infancy to old age, of which a description has been already given, (p. 644.).
The qffice of the uterus in parturition,— The act of parturition, or that process by which, in normal cases, the product of conception, after due development, is spontaneously sepa rated and expelled from the parent body, con stitutes the last chief office of the uterus.
The labour process may be regarded as es sentially a contest between two opposing forces, which are resisting on the one hand, and propulsive on the other. Resistance is necessary to preserve the fcetus in its place. Propulsion is requisite to detach and expel it from the parent body. The resisting force is chiefly passive in its operation. It is that which is offered by the membranes enclosing the fcetus, by the os and cervix uteri, by the soft parts lining and closing in the pelvis, and lastly by the osseous and ligarnentous struc tures of the pelvis itself. Naturally, these are sufficient to counteract any tendency to the escape of the fcetus from the operation of gravity upon it, in various changes of posture, or under any impulsive movements of the parent body. Their combined resistance is such as to require the operation of powerful mus cles to overcome them before the child can be expelled. This power is supplied by the uterus, aided subsequently by the diaphragm and other muscles, abdominal and pelvic. Labour constitutes the performance, and birth the end of the process, for the accomplishment of which in a natural manner the forces should be nearly evenly balanced. The preponde rance of power being, however, at first, on the side of resistance, and finally on that of pro pulsion. Whenever the forces are thus pro portioned, the act of parturition is, eceteris paribus, natural. Whenever they are greatly disproportioned, the process is abnormal ; whether the error be on the side of too much resistance, or too little propulsive force. In these last two particulars may be compre hended the history of every unnatural labour in which the mechanism* is at fault.
When labour is about to commence, the uterus having previously taken a lower posi tion in the pelvis, begins to contract gently, and often without pain, so that the only or chief evidence of its action is an occasionally recurring tension and hardness of the organ.
These contractions commence apparently at the cervix, so far as it is possible to analyse thern, and travel onwards to%ards the fun dus *: the IA hole organ soon becoming firm and resisting to the touch, and its upper part rising and assuming a more prominent posi tion in the abdomen. This hardness and tension is occasioned partly by the rigidity of the whole fibre, in a state of tonic contraction, and partly by the resistance offered by the in compressible contents of the organ, for w hich there is no exit so long as the cervix remains closed.