Page:The Works of William Harvey (part 1 of 2).djvu/623

 crease the area of the hypogastric region. When all these circumstances concur, it is quite clear that delivery is not far distant. Nature, in her provident care, contrives this dilatation of the parts in order that the fœtus may come into the world like the ripe fruit of a tree; just as she fills the breasts of the mother with milk that the being who is soon to enjoy an independent existence may have whereon to subsist. These, then, are the circumstances which immediately precede birth; and thus it happens that the presence of milk has especially been regarded as a sign of approaching delivery—milk, I mean, of a character suitable for the sustenance of the offspring; and this, according to Aristotle, is only visible at the period of birth; it is therefore never observed before the seventh month of pregnancy.

Fabricius maintains that on the subject of parturition there were two special heads of inquiry, viz. the time at which and the manner in which the process took place. Under the first of these heads he considers the term of utero-gestation; under the second, the way in which the fœtus comes into the world.

Aristotle thought that the term of utero-gestation varied much. "There is," he says, "a certain definite term to each animal, determined in the majority of cases by the animal's duration of life; for it follows of necessity that a longer period is required for the production of the longer-lived animals." He attributes, however, the chief cause to the size of the animal; "for it is scarcely possible," he continues, "that the vast frames of animals or of aught else can be brought to perfection in a short period of time. Hence it is that in the case of mares and animals of cognate species, though their duration of life is small, their term of utero-gestation is considerable; and thus the elephant carries its young for the space of two years, the reason being its enormous size, for each animal has a definite magnitude, beyond which it cannot pass." I would add, that the material of which each is formed has also its fixed limit in point of quantity. He says, moreover, "There is good reason why animals should have the periods of gestation, generation, and duration of life in certain cycles—I mean by cycle, a day, night, month, and year, and