This great physician supposes, that the seed of the male is a secretion of the strongest and most essential parts of all that is humid in the human body; and he thus explains how this secretion is made: "Venæ & nervi, he says, ab omni corpore in pudendum vergunt, quibus dum aliquantulum teruntur & calescunt ac implentur, velut pruritus incidit, ex hoc toti corpori voluptas ac caliditas accidit; quum vero pudendum teritur & homo movetur, humidum in corpore calescit ac diffunditur, & a motu conquassatur ac spumescit, quemadmodum alii humores omnes conquassati spumescunt.
"Sic autem in homine ab humido spumescente id quod robustissimum est ac pinguissimum secernitur, & ad medullam spinalem venit; tendunt enim in hanc ex omni corpore viæ, & diffundunt ex cerebro in lumbus ac in totum corpus & in medullum; & ex ipsa medull proacedunt viæ, ut & ad ipsum humidum perferatur & ex ipsa secedat; postquam autem ad hanc medullam genitura pervenerit, procedit ad renes, hac enim via tendit per venas, & si renes fuerint exulcerati, aliquando etiam sanguis defertur: a renibus autem transit per medois testes in pudendum, proce dit autem non qua urina, erum alia ipsi via est illi contigua, &c."[B]
[B] See Fæsius's Translation, vol. I. page 129.
Anatomists will no doubt discover that Hippocrates is not correct in tracing the road of the seminal liquor; but that does not affect his opinion, that the semen comes from every part of the body, and particularly the head, because, he says, those whose veins have been cut which lie near the ears only bring forth a weak, and very often an unfertile semen. The female has also a seminal fluid, which she emits, sometimes within the matrix, and sometimes without, when the internal orifice is more open than it should. The semen of the male enters into the matrix, where it mixes with that of the female; and as each has two kinds of fluid, the one strong and the other weak, if both furnish their strong, a male will be the result, and if their weak, a female; and if in the mixture there are more particles of the male liquor than the female, then the infant will have a greater resemblance to the father than to the mother, and so on the contrary. It might here be asked Hippocrates what would happen when the one furnished its weak semen and the other its strong? I cannot conceive what answer he could make, and that alone is sufficient to cause his opinion of two seeds in each sex to be rejected.
In this manner then, according to him, the formation of the fœtus is made: the seminal fluids first mix in the matrix, where they gradually thicken by the heat of the body of the mother; the mixture receives and attracts the spirit of the heat, and when too warm part of the heat flies out, and the respiration of the mother sends a colder spirit in; thus alternatively a cold and a hot spirit enter the mixture, which give life, and cause a pellicle to grow on the surface, which takes a round form, because the spirits, acting as a centre, extend it equally on all sides. "I have seen, says this great man, a fœtus of six days old; it was a ball of liquor surrounded with a pellicle; the liquor was reddish, and the pellicle was spread over with vessels, some red and others white, in the midst of which was a small eminence, which I thought to be the umbilical vessels, by which the fœtus receives nourishment and the spirit of respiration from the mother. By degrees another pellicle is formed, which surrounds the first; the menstrual blood, being suppressed, abundantly supplies it with nutriment, and which coagulates by degrees, and becomes flesh; this flesh articulates itself in proportion as it grows, and receives its form from the spirit; each part proceeds to take its proper place; the solid particles go to their respective situations and the fluid to theirs: each matter seeks for that which is most like itself, and the fœtus is at length entirely formed by these causes and these means."
This system is less obscure and more reasonable than that of Aristotle, because Hippocrates endeavours to explain every matter by particular reasons: he borrows from the philosophy of his times but one single principle, which is, that heat and cold produce spirits, and that those spirits have the power of ordering and arranging matter. He has viewed generation more like a physician than a philosopher, while Aristotle has explained it more like a metaphysician than a naturalist; which makes the defects of Hippocrates's system particular and less apparent, while those of Aristotle's are general and evident.
These two great men have each had their followers; almost all the scholastic philosophers, by adopting Aristotle's philosophy, received his system of generation, while almost every physician followed the opinion of Hippocrates; and seventeen or eighteen centuries passed without any thing new being said on the subject. At last, at the restoration of literature, some anatomists turned their eyes on generation, and Fabricius Aquapendente was the first who made experiments and observations on the impregnation and growth of the eggs of a fowl. The following is the substance of his observations.
He distinguished two parts in the matrix of a hen, the one superior and the other inferior. The superior he calls the Ovarium, which is properly no other than a cluster of small yellow eggs of a round form, varying in size from the bigness of a mustard-seed to that of a large nut or medlar. These small eggs are fastened together by one common pellicle, and form a body which nearly resembles a bunch of grapes. The smallest of these eggs are white, and they take another colour in proportion as they increase.
Having examined these eggs immediately after the communication of the cock, he did not perceive any remarkable difference, nor any of the male semen in any one of these eggs; he therefore supposed that every egg, and the ovarium itself, became fruitful by a subtle spirit, which came from the semen of the male; and he says, that in order to secure this fecundating spirit, nature has placed at the external orifice of the vagina of birds a kind of net-work or membrane, which permits, like a valve, the entrance of this seminal spirit, but at the same time prevents it from re-issuing or evaporating.
When the egg is loosened from the common pellicle, it descends by degrees through a winding passage into the internal part of the matrix. This passage is filled with a liquor nearly similar to the white of an egg; it is also in this part that the eggs begin to be surrounded with this white liquor, with the membrane which occasions it, the two ligaments (chalazæ) which passes over the white, and connects it with the yolk and shell, which are formed in a very short time before they are laid. These ligaments, according to Fabricius, is the part of the egg fecundated by the seminal spirit of the male; and it is here where the fœtus first begins to form. The egg is not only the true matrix, that is to say, the place of the formation of the chick, but it is from the egg all generation depends. The egg produces it as the agent: it supplies both the matter and the organs; the ligaments are the substance of formation; the white and the yolk are the nutriment, and the seminal spirit of the male is the efficient cause. This spirit communicates to the ligaments at first an alterative faculty, afterwards a formative, and lastly the power of augmentation, &c.