Before the action of this external heat, not the least appearance of blood is to be seen; and it is not till twenty-four hours after, that I have perceived any change in the colour of the vessels. The blood first appears in the placenta, which communicates with the body of the chicken: but this blood seems to lose its colour as it approaches the body of the animal; for the chicken is entirely white, and we with difficulty discover in the first, second, and third days after incubation, a few small sanguinary points which are close to the body of the animal, but which seem not to make part of it, although it is these sanguinary points which afterwards form the heart. Thus, the formation of the blood is a change occasioned in the liquors by the motion heat communicates to them, and this blood is formed even out of the body of the animal, the whole substance of which is then only a kind of mucilage, or thick jelly.
The fœtus, as well as the placenta, derives the necessary nutriment for expansion, by a kind of absorption, and they assimilate the organic parts of the liquor in which they float: for the placenta cannot be said to nourish the animal, no more than the animal nourishes the placenta; since, if the one nourished the other, the first would soon appear to diminish, while the other increased, whereas both increase together, I have indeed observed in eggs, that the placenta at first increases much more in proportion than the fœtus, and therefore it may nourish the animal, or rather convey the nutriment to it, by intussusception.
What we have just said concerning the chicken, is easily applied to the human fœtus, which is formed by the union of the organic molecules of the two sexes. The membranes, and placenta, are formed from the superabundance of the particles which have entered into the composition of the embryo: which is then inclosed in a double membrane, where there is also a quantity of liquor, which is, perhaps, at first, but a portion of the semen of the father and the mother; and as the fœtus does not quit the matrix, it enjoys, from the instant even of its formation, an external heat necessary for its expansion; this heat communicates a motion to liquors, and sets the organs in play, and blood is formed in the placenta, and in the body of the embryo, by the motion occasioned by this heat. It may be even said, that the formation of the blood of the infant is as independent of the mother, as that which passes into the egg, is of the hen which hatches it, or of the oven which heats it.
It is certain, that the fœtus, placenta, and membranes, grow by intussusception: for, in the earliest days of conception, the pouch, which contains the whole product of generation, is not adherent to the matrix. De Graaf, in his experiments on doe rabbits, made these globules, wherein the whole business of generation lies, move about in the matrix. Thus, in the first stages, they increase and grow by drawing nutriment from the liquors which bathe the matrix, to which they are afterwards attached by a mucilage, in which small vessels are formed with time, as we shall hereafter explain.
But, not to quit the subject, let us return to the immediate formation of the fœtus, on which there are many remarks to be made, both as to its situation, and the different circumstances which may prevent or stop its formation.
In the human species, the seed of the male enters into the matrix, the cavity of which is considerable; and when it meets with a sufficient quantity of female semen, a mixture of the organic particles succeed, and the formation of the fœtus ensues: the whole, perhaps, is done instantaneously, especially if the liquors are both in an active and flourishing state. The place where the fœtus is formed, is the cavity of the matrix, because the seed of the male can enter there more easily than into the trunks; and as this viscera has but one small orifice, which is always shut, excepting when the ardour of love causes it to open, the materials of generation remain there with safety, and scarcely ever reissue but by rare and unfrequent circumstances: but as the liquor of the male sprinkles the vagina, before it penetrates the matrix, by the activity of the organic molecules which compose it, it may go farther into the trunks, and, perhaps, into the ovarium. As the liquor of the female has already its perfection in the glandular bodies of the testicles, from which it flows and moistens the trunks and other parts before it descends into the matrix, and as it may issue out of the vacuities left around the neck of the matrix, it is not impossible, that the mixture of the two liquors may be made in all these different places. It is, therefore, probable that fœtuses are often formed in the vagina, but which fall out as soon as they are formed, because there is nothing to retain them. It may also sometimes happen, that fœtuses are formed in the trunks; but this case is very rare, and cannot happen but when the seminal liquor of the male enters the matrix in great plenty.
The collection of anatomical observations makes mention of fœtuses not only being found in the trunks, but also in the testicles. In the History of the Old Academy of Sciences, (vol. II. page 91.) we meet with an observation on this subject. M. Theroude, a surgeon at Paris, shewed the academy an unformed mass, which he found in the right testicle of a girl of eighteen years of age. In it were two open slits, furnished with hair like two eye-lids, above which was a kind of forehead, with a black line instead of eyebrows; immediately over that were many hairs matted together in two separate lines, one of which was seven, and the other three inches long; under the great angle of the eye, two of the grinding teeth appeared to shoot, hard, thick, and white; they had their prongs, and a third tooth thicker than the rest above them. There appeared likewise other teeth at different distances from each other: two between these, of the canine nature, issued from an opening where the ear is placed. In the same volume, page 144, it is related, that M. Mery found, in the testicle of a woman who had conceived, a bone of the upper jaw, with many teeth therein, so perfect that some appeared to be of more than ten years growth. We find, in the Journal de Medicine, for January 1683, published by the Abbé de la Roque, the history of a lady who died with the ninth child, which was formed in or near one of the testicles, which is not very clearly explained. The fœtus was about an inch in size, completely formed, and the sex easily to be distinguished. We also find, in the Philosophical Transactions, some observations on the testicles of women, wherein teeth, hair, and bones, have been found. If all these circumstances are true, we must suppose, that the seminal liquor of the male sometimes ascends, although very seldom, to the testicles of the female. Yet, notwithstanding all this, I have some difficulty to believe it; first, because the circumstances, which appear to prove it, are extremely rare: secondly, because a perfect fœtus has never been seen in the testicles but by M. Littre, who seems to relate it in a very suspicious manner: thirdly, because it is not impossible, that the seminal liquor of the female alone may produce organized masses, as moles, hair, bones, flesh, and, in short, because if we give credit to anatomists, fœtuses may be formed in the testicles of men, as well as in those of women: for we find, in the History of the Royal Academy, vol. II. p. 298, an observation of a surgeon, who says, he discovered in the scrotum of a man, the figure of a child inclosed in his membranes: and that the head, feet, eyes, bones, and cartilages, were distinguishable. If all these observations were equally true, we must necessarily adopt one of these two hypotheses, either that the seminal liquor, of each sex, cannot produce any thing without being mixed with that of the other sex, or that either of them can produce irregular masses of itself. By keeping to the first, we should be obliged to admit, to explain in all the circumstances we have related, that the liquor of the male sometimes ascends to the testicle, and, by mixing with the seminal liquor of the female, forms organized bodies; and so may also the female fluid, by being plentiful in the vagina, penetrate, during the time of copulation, into the scrotum of the male, nearly as the venereal virus often reaches that part; and that in this case, an organized body may be found in the scrotum, by the mixture of the male and female fluids; or, if we admit the other hypothesis, which appears to be the most probable, and suppose, that the seminal liquor of each individual may produce organized masses, then we may be able to say, that all these bony, fleshy, and hairy productions, sometimes found in the testicles of females, and in the scrotum of males, may derive their origin from the liquor of the individual in which they are found. But enough of observations upon facts, which appear to be as uncertain as inexplicable, for I am much inclined to believe, that, in certain circumstances, the seminal liquor of each individual may produce something alone and of itself, and that young girls might form moles without any communication with the male, as hens form eggs without having received the cock. I might support this opinion with observations which appear to me as credible as those I have quoted. M. de la Saone, physician and anatomist of the Academy of Sciences, published a memoir on this subject, in which he asserts, that religious nuns, though strictly cloistered, had formed moles. Why should that be impossible, since hens form eggs without communication with the cock? and in the cicatrice of these eggs we perceive a mole, with appendages, instead of a chicken? The analogy appears to me to have sufficient power for us, at least to doubt, or suspend our determination. Be this as it will, it is certain that the mixture of the two liquors are required to form a fœtus , and that this mixture cannot come to any effect but when it is in the matrix, where the anatomists have sometimes found fœtuses; and it is natural to imagine, that those which have been found out of the matrix, and in the cavity of the abdomen, have escaped by the extremity of the trunks, or by some accidental opening, and that they never fall from the testicles into the abdomen, because it is almost an impossibility that the seminal liquor of the male can ascend so high. Leeuwenhoek has computed the motion of these pretended spermatic animals to be four or five inches in forty minutes, which would be more than sufficient for the animalcules to traverse from the vagina into the matrix, from the matrix into the trunks, and from the trunks into the testicles, in an hour or two, provided all the liquor had that motion. But how is this to be conceived, that the organic molecules, whose motion ceases as soon as the liquid fails, can arrive as far as the testicles, unless brought there by the liquor in which they swim? This progressive motion cannot be given by the organic molecules to the liquor which it contains, therefore, whatever activity these molecules may be supposed to have, we cannot see how they can arrive at the testicles, and form a fœtus there, unless the liquor itself was pumped up and attracted thither, a supposition not only gratuitous but even against all human probability.
The doubts which this supposition gives rise to, confirm the opinion that the male fluid penetrates the matrix, and enters therein by the orifice, or across the membraneous coat of the viscera. The female fluid may also enter into the matrix, either by the opening at the upper extremity of the trunks, or across the skin even of the trunks and matrix. M. de Weirbrech, an able anatomist of Petersburg, confirms this opinion:——"Res omni attentione dignissima (says he) oblata mihi est in utero feminæ alicujus a me dissectæ; erat uterus ea magnitudine qua esse solet in virginibus, tubæque ambæ apertæ quidem ad ingressum uteri, ita ut ex hoc in illas cum specillo facile possem transire ac flatum injicere, sed in turbarum extremo nulla dabatur apertura, nullus aditus; fimbriarum enim ne vestigium quidem aderat, sed loco illarum bulbus aliquis pyriformis materia subalbida fluida turgens, in cujus medio fibra plana nervea, cicatriculæ æmula, apparebat, quæ sub ligamentuli specie usque ad ovarii involucra protendebatur.
"Dices, eadem a Regnero de Graaf jam olim notata. Equidem non negaverim illustrem hunc prosectorem in libro suo de organis mulieribus non modo similem tubam delineasse, Tabula XIX, fig. 3, sed & monuisse, 'tubas quamvis secundum ordinariam naturæ dispositionem in extremitate sua notabilem semper coarctationem habeant, præter naturam tamen aliquando claudi;' verum enimvero cum non meminerit auctor an id in utraque tuba ita deprehenderit; an in virgine; an status iste præternaturalis sterilitatem inducat: an vero conceptio nihilominus fieri possit; an a principio vitæ talis structura suam originem ducat; sive an tractu tempora ita degenerare tubæ possint; facile perspicimus multa nobis relicta esse problemata quæ, utcumque soluta, multum negotii facessant in exemplo nostro. Erat enim hæc femina maritata, viginti quatuor annos nata, quæ filium pepererat quem vidi ipse, octo jam annos natum. Dic igitur tubas ab incunabulis clausas sterilitatem inducere: quare hæc nostra femina peperit? Dic concepisse tubis clausis; quomodo ovulum ingredi tubam potuit? Dic coaluisse tubas post partum: quomodo id nosti? Quomodo adeo evanescere in utroque latere fimbriæ possunt, tanquam nunquam adfuissent? Si quidem ex ovario ad tubas alia daretur via, præter illarum orificium, unico gressu omnes superarentur difficultates; sed fictiones intellectum quidem adjuvant, rei veritatem non demonstrant; præstat igitur ignorationem fateri, quam speculationibus indulgere[AD]." The difficulties which occurred to this able author are insurmountable in the egg system, but which disappear in our explanation. This observation seems only to prove what we have observed, that the seminal liquor of both male and female may penetrate the coat of the matrix, and enter across the pores of the membranes; to be assured of it, it is only necessary to pay attention to the alteration that the seminal liquor of the male causes to the viscera, and to the kind of vegetation or expansion that it causes there. Besides, the liquor which issues by the vacuities of De Graaf, being of the same nature as the liquor of the glandular bodies, it is very evident that this liquor comes from the testicles, and yet there is no vessel through which it can pass; consequently we must conclude, that it penetrates the spongy coat of all these parts, and that it not only enters the matrix, but even can issue out when these parts are in irritation.