Page:The Works of William Harvey (part 1 of 2).djvu/632

 same thing happens to the fruit of the womb; it depends on the abundance or deficiency of nutriment, on the strength or weakness of body, and on the right or wrong ordering of life with reference to what physicians call the "non-naturals," whether the child arrives sooner or later at maturity, i.e. is born.

Fabricius describes the manner of parturition as follows: "The uterus having been so enlarged by the bulk of the fœtus that it will admit of no further distension without risk, and thus excited to expulsion, is drawn into itself by the action of the transverse fibres, and diminishes its cavity. Thus whilst previously neither the excrementitious matters from their quantity, nor the fœtus from its bulk, could be contained within it, the uterus, contracted and compressed as it is now, becomes still less able to retain them. Wherefore, first of all, the membranes, as being the weaker parts, and suffering most pressure, are ruptured, and give exit to the waters, which are of a very fluid consistence, for the purpose of lubricating the passages. Then follows the fœtus, which tends towards, and, as it were, assaults the uterine aperture, not only by the force of its own gravity as no longer floating in water, but compressed and propelled by the action of the uterus: the abdominal muscles and the diaphragm also assist mightily in the entire process."

Now in these words Fabricius rather describes the process of defæcation or an abortion than a genuine and natural birth. For although in women, as a general rule, the membranes are ruptured before the escape of the fœtus, it is not universally so; nor does it hold in the case of other animals which bring forth their young enveloped in their membranes. This can be observed in the bitch, ewe, mare, and others, and more particularly in the viper, which conceives an ovum of an uniform colour and soft shell (resembling in fact the product of conception in the woman); this is retained until the fœtus is completely formed; it is then expelled entire, and, according to Aristotle, is broken through by the young animal on the third day. It sometimes happens, however, that kittens, whilst yet in utero, gnaw through the membranes, and so come into the world uninvolved.