A famous experiment, in favour of the egg system, is supplied by De Nuck; he opened a bitch three days after copulation; he drew out one of the horns of the matrix, and made a ligature in the middle, so that the upper part of the passage could have no communication with the lower; after which he replaced this horn, and closed up the wound, with which the bitch seemed but little incommoded. At the end of twenty-one days he opened it again, and found two fœtuses in the upper part, that is between the testicles and the ligature; but in the lower part there was no fœtus. In the other horn of the matrix, which had not been tied by a ligature, he found three fœtuses, which were regularly disposed, which proves, he says, that the fœtus does not proceed from the seed of the male, but exists in the female egg. Supposing this experiment, which has only been made once, was always followed with the same effect, we should not then be right in concluding that fecundation is made in the ovary, and that eggs are detached therefrom which contain the fœtus completely formed. It would only prove that the fœtus may be formed in the upper parts of the horns of the matrix as well as in the lower; and it seems very natural to imagine that the ligature, compressing the middle of the horns of the matrix, impelled the seminal liquors, which are in the lower parts, to issue out, and thus destroy the business of generation in them.
Thus we have gone through the opinions of anatomists and physicians on the subject of generation; and it now only remains for me to recount what I have been enabled to draw from my own researches and experiments, and it will then be seen whether my system is not infinitely more agreeable to Nature than any of those I have given an account of.
EXPERIMENTS ON THE METHOD OF GENERATION.
I often reflected on the above system, and was every day more and more convinced that my theory was infinitely the most probable. I then began to suppose that, by a microscope, I might be able to attain a discovery of the living organic particles, from which I thought every animal and vegetable drew their origin. My first supposition was, that the spermatic animalcules seen in the seed of every male, might possibly be these organic particles; on which I reasoned as follows:
If every animal and vegetable contain a quantity of living organic particles, these particles would be found in their seed, and in a greater quantity than in any other substance, because the seed is an extract of what is most analogous to the individual, and the most organic; and the animalcule we see in the seed of males are, perhaps, only these same living organic molecules, or at least the first union, or assemblage of them. But if this is so, the seed of the female must also contain similar living organic molecules, and, consequently, we ought to find moving bodies there as well as in the male: and since the living organic particles are common both to animals and vegetables, we should also find them in the seeds of plants, in the nectarium, and in the stamina, which are the most essential parts of vegetables, and which contain the organic molecules necessary for reproduction. I then seriously thought of examining the seminal liquors of both sexes, and the germs of plants, with a microscope. I thought, likewise, that the reservoirs of the female seed might possibly be the cavities of the glandular bodies, in which Valisnieri and others had uselessly sought for the egg; and at length determined to undertake a course of observations and experiments. I first communicated my ideas to Mr. Needham, a gentleman well known for his microscopical observations, and read to him the first part of this work; he seemed to approve of these ideas, and did me the favour to lend me his microscope which was infinitely superior to my own. At the same time I communicated my system and project of experiments to Messrs. Daubenton, Gueneau, and Dalibard, all of whom encouraged me to persevere in my determination, and from whom, in the course of making those experiments, I received much assistance, particularly from Mr. Daubenton.
Persons not experienced in the use of the microscope will not be displeased that I here insert some remarks which will be useful to them, if they repeat the following experiments, or make new ones. We should give the preference to double microscopes, in which we see objects perpendicularly, from their having a plain or concave mirror, which shews the objects clear; the concave mirror is the most preferable when the observations are made with the strongest lens. Leeuwenhoek, who undoubtedly has been the greatest and most indefatigable of all microscopical observators, is said to have only made use of simple microscopes, with which he viewed objects horizontally. If this is true, it is necessary to remark, that most of the plates given by Leeuwenhoek of microscopical objects, especially spermatic animals, represents them much thicker and longer than he really saw them, which renders the microscopes we speak of preferable to the horizontal, as they are more stable; the motion of the hand, with which the microscope is held, producing a little trembling, which causes the object to appear wavering, and never presents the same part for any time. Besides, there is always a motion in the liquors caused by the agitation of the external air, at least, if we do not put the liquor between two plates of glass, or even fine talc, which diminishes somewhat of its transparency, and greatly lengthens the experiment; but the horizontal microscope, whose tables are vertical, has the still greater inconvenience, that the most ponderous parts of the drop of liquor fall to the bottom; consequently there are three motions, that of the trembling of the hand, the agitation of the fluid by the action of the air, and also that of the parts of the liquor falling to the bottom: from the combination of which, certain small globules, which we see in these liquors, may appear to move by their own motion and powers, while they only obey the compounded power of those three causes.
When we put a drop of liquor on the table of the double microscope, although horizontally placed, and in the most advantageous situation, we still see one common motion in the liquor, which forces all what it contains to one side. We must wait till the fluid is in an equilibrium and at rest, before we make our observations; for it often occurs, that this motion of the fluid hurries away many globules, and forms a kind of whirling motion, which returns one of these globules in a very different direction to the others. The eye is then fixed on the globules, and seeing one take a different course from the rest, supposes it an animal, or at least a body, which moves of itself, whereas its motion is only owing to that of the fluid; and as the liquor is apt to dry and thicken in the circumference of the drop, endeavours must be made to fix the lens on the centre of it. The drop should also be as large as possible, and contain as much liquor as will permit a sufficient transparency, to see perfectly what it contains.