Read Ebook: Buffon's Natural History Volume 03 (of 10) Containing a Theory of the Earth a General History of Man of the Brute Creation and of Vegetables Minerals &c. &c. by Buffon Georges Louis Leclerc Comte De Barr James Smith Editor

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These glandular substances are not of the same colour in every sow, in some they are red, in others more clear; and they are of all sizes, from the most minute point to that of a grape. On opening them we find a triangular cavity filled with a limpid liquor, which coagulates by the fire, and becomes white like that contained in the vesicles. Valisnieri hoped to meet with the egg in one of those cavities, but although he sought for it with the utmost assiduity in the glandular substance of the ovaries of four different sows, and afterwards in those of other animals, yet he could never discover the egg which Malpighius asserts to have met with once or twice.

Below these glandular substances the vesicles of the ovary were seen, and which were in a greater or lesser number as the glandular substances are thicker or smaller, for in proportion as the glandular substances increase, the vesicles diminish. Some of these vesicles were the size of a lentil, and others as small as a millet-seed. In crude testicles twenty, thirty, or thirty-five vesicles might be counted, but when boiled a greater number are seen; and they are so strongly connected by fibres and membraneous vessels, that it is impossible to separate them without a rupture.

Having examined the testicles of a sow which never had littered, he found there, as in the rest, glandular bodies, and their triangular cavities filled with lymph, but never met with the egg either in the one or the other. The vesicles of this sow which had never littered were greater in number than in those which had littered or conceived. In the testicles of another sow which had conceived, and whose young were much expanded, he found two large glandular substances, that were empty, and others smaller, in their common state. Having also dissected many others when with young, he found that the number of glandular substances was always greater than that of the foetus, which confirms our observations on De Graaf's experiments, and proves they are not exact; what he terms the follicules of the ovary being only the glandular substances, whose number always exceed that of the foetus. In the ovaries of a sow but a few months old, the testicles were large, and sprinkled with vesicles pretty well tumefied: between these vesicles there were four rising glandular substances in one of the testicles, and more in the other.

After having finished his experiments on sows, Valisnieri repeated those of Malpighius on the testicles of cows, and found that all he had said was conformable to truth; only Valisnieri owns that he has never been able to find the egg which Malpighius thought he had seen once or twice in the internal cavity of glandular bodies. Valisnieri proceeded in his experiments upon a variety of other animals to discover this egg, but in vain; nevertheless his prejudice for that system induced him, contrary to his experience, to admit the existence of eggs, which neither he nor any other man ever did or ever will see. It is scarcely possible to make a greater number of experiments, or better than he has done. He observes, as something particular to a ewe, that there are never more glandular substances in the testicles than foetuses in the matrix. In young ewes, which have never been with the male, there is but one glandular substance in each testicle, which when worn away, another is found; and if a ewe has only one foetus in her matrix, there is but one glandular substance in the testicles; if there are two foetuses there will be two glandular substances. This substance occupies the greatest part of the testicles; after it disappears another is formed for the purpose of another generation.

In the testicles of a she-ass he perceived vesicles the size of small cherries, which evidently prove they are not eggs, since, being of that size, they could not enter into the horns of the matrix, which are too narrow in this animal for their reception.

The testicles of a female dog, wolf, or fox, have a kind of cowl, or covering, which is produced by the expansion of the membrane that surrounds the horns of the matrix. In a bitch, whose heat was just began, and had not been brought to a dog, Valisnieri found this cowl, which is not adherent to the testicle, internally bathed with a liquor like whey: he discovered also two glandular substances in the right testicle, which run almost its whole length. These glandular substances had each a small nipple, with a little orifice, from which of itself issued a clear liquor like whey, and when pressed, a greater quantity came out, which made him imagine, that this liquor was the same as that found within the cowl: he blew into this orifice, by the means of a small pipe, and immediately the glandular body was puffed up; and having introduced a bristle, he easily penetrated to the end of it: he opened this glandular substance the same way as the bristle was entered, and found within a cavity which communicated with the orifice, and which also contained a good deal of liquor. Valisnieri was also in hopes to discover the egg, but, notwithstanding all his endeavours and strict attention, he never could perceive it. He remarked, that the extremity of these nipples, from which this liquor flowed, was contracted by a sphincter, which served to shut up, or open the orifice of the nipple: he found also in the left testicle two glandular bodies with the like cavities, nipples, orifices, and liquor distilling from them. Still not being able to find the egg, neither in this liquor, nor in the cavity which contained it, he boiled two of these glandular substances, hoping that by this means he might discover the object he was in pursuit of, but it was all in vain.

After this he opened another bitch whose heat was off, and having introduced air between the testicle and its covering, he found it dilated like a bladder by means of inflation; having raised this cowl, he found three glandular substances on the testicle, but they had no apparent nipple, nor orifice, nor did any liquor distil from them.

In another bitch that had pupped two months, and had five puppies, he found five glandular substances, which were become very small, and began to obliterate, without leaving any cicatrices: there still remained a small cavity in the middle, but it was dry and empty.

Not content with these, and many more experiments, Valisnieri, who would not give up his researches after the pretended egg, called together the most expert anatomists of his country, among whom was M. Morgagni, and having opened a young bitch at the time of her first heat, and had been with a male three days before, they examined the vesicles of the testicles, the glandular substances with their nipples, orifice, and liquor which flowed from them, and in their internal cavities, but not an egg was to be found. After this he made experiments on female goats, foxes, cats, and a great number of mice, &c. He always found vesicles in the testicles of all those animals, and often the glandular substances, and the liquor they contained, but never any egg.

At length, desirous of examining the testicles of a woman, he had an opportunity of opening a farmer's wife, a young woman that was killed by a fall from a tree. She had been married several years, but although of a good habit of body, yet she had never borne a child. He sought if the cause of her sterility was not discoverable in the testicles; and he found the vesicles all replete with a blackish and corrupted matter.

In the testicles of a girl of eighteen, who had been brought up in a convent, and, according to all appearances, was a virgin, he found the right testicle somewhat larger than the left: its shape was oval, and its surface a little unequal. This inequality was produced by the protuberance of five or six vesicles of this testicle which advanced forwards; one of which was more prominent than any of the rest. Having opened this vesicle, a spirit of lymph issued out: around it there was a glandular substance in form of a crescent of a yellowish colour rather bordering on the red. He cut the remainder part of the testicle transversely, and found many vesicles filled with a limpid liquor, and remarked that the corresponding trunk to this testicle was very red and a little longer than the other, as he had frequently observed in female animals, when in their amorous season.

The left testicle was as round as the right, it was whiter, and its surface more smooth; for although there were some vesicles a little prominent, yet there were not any in form of a nipple; they were all alike, without any glandular substance, and the corresponding trunk was neither inflamed nor red.

In a little girl of five years old, he found the testicles with the vesicles, blood vessels, fibres and nerves complete.

In the testicles of a woman sixty years of age, he found some vesicles, and the vestiges of a glandular substance, which were as so many thick points of matter of a dark brownish colour.

From all these observations Valisnieri concludes, that the business of generation is carried on in the female testicles, which he looked upon as ovaries, although he never found any eggs in them, but on the contrary, evidently saw that the vesicles were not eggs. He also says, that it is not necessary for the seed of the male to enter into the matrix to impregnate the egg: he supposes that the egg comes from the nipple of the glandular substance, after impregnation in the ovarium; that from thence it falls into the trunk, and descends by degrees, till at last it fastens to the matrix. He adds, he is persuaded that the egg is concealed in the glandular substance, and that all the business of generation is performed in the cavity, although neither he nor any other anatomist, have ever seen or been able to find it.

According to Valisnieri the spirit of the male seed ascends to the ovarium, forces its way into the egg, and gives motion to the foetus that pre-exists therein. In the ovarium of the first woman were eggs, which not only inclosed in miniature every child she brought forth, but of the whole human race. That if we cannot conceive this infinite chain of individuals contained in one, it is the fault of our minds, the weakness of which is every day perceptible; but it is, upon that account, no less true, that every animal which has been, is, and will be, were created all at one time, and inclosed in the first females. The resemblance of children to parents only proceeds, continues he, from the imagination of the mother, the power of which is so great on the foetus that it can produce on it spots, marks, disproportions, and extraordinary births, as well as perfect resemblances.

This system of the eggs, which is unreasonable, and without foundation, would, nevertheless, have obtained the unanimous suffrages of all physicians, if, when it was first endeavoured to be established, another system had not been formed on the discovery of spermatic animals.

This discovery, for which we are indebted to Leeuwenhoeck and Hartsoeker, has been confirmed by Andri, Valisnieri, Bourguet, and many other observers of Nature. I shall relate what has been said concerning the spermatic animals which are found in the seminal liquor of all males: they are in such vast numbers that the semen seems to be entirely composed of them; and Leeuwenhoeck pretends to have seen many millions of them in a drop smaller than the smallest grain of sand. Although we do not meet with any in female animals they abound in all males, both in the semen emitted naturally and that in the testicles, as well as in the seminal vesicles. If the semen of a man is exposed to a moderate heat it thickens, and the motions of all the animalcules immediately cease, but if allowed to cool it becomes thinner, and the animals preserve their motion till the liquor thickens as it dries away. The thinner the liquor becomes the more the animalcule increase, and if water is added it will appear like a substance of small animals. When the motion of these animalcule is nearly finished, whether from heat, or any other cause, they seem to assemble closer together, and have a whirling motion in the centre of a small drop which may have been taken out for observation, and appear all to perish at one and the same time, whereas in the larger portion of the liquor they are easily seen to perish successively.

See Veerheyen, sup. anat. tom. ii. page 69.

Leeuwenhoeck observed, in the semen of a cock, animals which resemble the figure of an eel, but so exceedingly minute, that he pretends fifty thousand would not equal in size a grain of sand; and in that of a rat many millions would be required to make the thickness of a hair, &c. This observer imagined that the whole substance of the semen was only a mass of these animalcules. He perceived these animalculae in the semen of men, quadrupeds, birds, fishes, insects, &c. In that of grasshoppers they were long and slender. They are attached, he says, by their extremities, and the inferior of which he calls the tail, had a quick motion, like that of the tail of a serpent, when the upper part is motionless. He further adds, that in the semen of young animals the animalculae are motionless, but as the age for reproduction comes on they move about with great vivacity.

In the semen of a male frog he observed animalculae, at first they were imperfect and motionless, but some time afterwards he found them living: they were so very small, he says, that ten thousand would scarcely equal the size of a single egg of the female. It was only those in the seminal liquor of the frog which had life and motion.

In the semen of a man, and that of a dog, he pretends to have seen two kinds, which he looked upon as males and females. Having inclosed the seed of a dog in a vial, he says, that numbers of the animalculae died the first day; the second and third there died still more, and very few remained alive the fourth. But having repeated this experiment on the semen of the same dog, he found, at the end of seven days, live animalculae, some of which swam with as much swiftness as in fresh-extracted semen; and having opened a bitch which had been three times with the same dog, he could not perceive by the naked eye any seminal liquor of the male in either of the horns of the matrix; but by help of a microscope he discovered the spermatic animals of the dog in both horns of the matrix, and great numbers of them in that part of the matrix adjoining to the vagina, which, says he, evidently proves that the male semen enters the matrix, or at least that the spermatic animals of the dog had got there by their own motion, which is sufficient to carry them four or five inches in half an hour. In the matrix of a doe rabbit, which had just received the buck, he likewise observed an infinite number of spermatic animals; he says, that their bodies are round, with long tails, and that they often change their forms, especially when the humid matter in which they swim evaporates and dries.

Leeuwenhoeck's experiments have been frequently repeated and found conformable to truth. There have been some inclined to exceed him in these discoveries. Dr. Dalenpatius having observed the seminal liquor of a man, not only pretended to have discovered animals like tadpoles, whose bodies appeared nearly the size of a grain of wheat, and their tails four or five times longer than their bodies, and which moved with great agility, but, what is still more marvellous, he observed one of these animals quit its covering; upon which it was no longer an animalcule, but had become a human body, the two legs of which, he affirms, were very discernible, as were the arms, breast, and head. But by the figures which this author has given of this pretended embryo, it is evident his assertion is false. He might suppose he saw what he relates, but he was mistaken; for the embryo, such as he describes, was more formed on quitting this covering, and the state of a spermatic worm, than it would have been at the end of a month or five weeks in the matrix of its mother; therefore this observation of Dalenpatius, instead of having been confirmed by other observations, has been rejected by every naturalist, the most exact and accurate of which have only discovered, in the seminal liquor of man, round and oblong bodies, which seemed to have long tails, but without any kind of members.

See Nouvelles de la Republique des Lettres, Ann. 1699, page 552.

Valisnieri and Bourguet, whom we have quoted, discovered small worms in the seed of a rabbit, one of whose extremities was thicker than the other; they were very lively and active, struck the liquor with their tails, and twisted and turned themselves like snakes. At last I clearly perceived them to be real animals, "e gli riconobbi, e gli giudicai senza dubitamento alcuno per veri, verissimi arciverissimi vermi." This author, who was prejudiced with the system of eggs, has, nevertheless, admitted of spermatic worms, and taken them for real animals.

M. Andry having made observations on these spermatic worms of a man, pretends that they are only found in the age proper for generation; that in the younger years, and in old age, they do not exist: that in those affected with venereal disorders there are very few, and those are languishing, and for the most part dead: that in impotent persons we do not see any alive; that these worms in the semen of men have larger heads than in that of other animals, which agrees, he says, with the figure of the foetus and the child; and he adds, those people who too frequently enjoy female amours, have generally but few or none of these animalcules in their semen.

Leeuwenhoeck, Andry, and many others, strenuously opposed the egg system; they had discovered in the semen of all males living animalcules; they proved that these animalcules could not be regarded merely as dwelling in this liquor, since their bulk was greater than that of the liquor itself; and that nothing like them was found either in the blood, or in the other animal liquors. They asserted, that females furnished nothing similar, nothing alive; and it was therefore evident that the fecundity attributed to them belonged, on the contrary, to males alone: and that the discovery of these spermatic animals in the semen tended more to the explanation of generation than all that had been before supposed; since, in fact, what was most difficult to conceive in generation, was the production of the living part, all the rest being only accessary operations, and therefore no doubt could remain but these little animals were destined to become men, or perfect animals of their kind. When it was opposed to the partizans of this system, that it did not seem natural to suppose that so many millions of animalcules, every one of which might become a human being, should be employed for a purpose of which one alone was to reap the advantage; when it was asked them, why this useless profusion of the shoots of human beings? they answered, that it was only consonant with the common munificence of nature: that out of many millions of seeds which plants and trees produce, but a very few succeed, and therefore we must not be surprised at the same circumstance in spermatic animals. When the infinite minuteness of the spermatic worm, compared to man, was objected to them, they answered, by the example of the seed of trees; and they added, with some foundation, metaphysical reasonings, by which they proved that great and small being only relations, the transition from small to great, or from great to small, was executed by nature with still more facility than we can conceive.

Besides, continue they, have we not very frequent examples of transformation in insects? do we not see small aquatic worms become winged animals, by only throwing off their coats, which were their apparent and external forms? and may not spermatic animals, by a similar transformation, become perfect animals? All therefore, they conclude, concurs to favour this system of generation, and confuting that founded on eggs; and if there are eggs in viviparous females, the same as in the oviparous, these eggs will only be the necessary matter for the growth of the spermatic worm, which enters into the egg by the pedicle that adheres to the ovarium, and where it meets with food ready prepared for it. All the worms which find not this passage through the pedicle into the egg will perish, and that one which alone has traced its way will arrive at its transformation. The difficulty of meeting with the passage in the pedicle of the egg, can only be compensated by the infinite number of spermatic worms. It is a million to one that any particular spermatic worm will meet with the pedicle of the egg, and therefore what at first appears a profusion is highly necessary. When one has entered, no other can introduce itself, because, say they, the first worm entirely shuts up the passage, or there is a valve at the entrance of the pedicle, which is free when the egg is not absolutely full; but when the worm has filled the egg, the valve can no longer open although impelled by another worm. This valve is very well imagined, because, if the first worm should chance to return, it opposes its egress, and obliges it to remain and undergo the transformation. The spermatic worm then becomes the foetus, the substance of the egg its food, the membranes, its covering, and when the nutriment in the egg is nearly exhausted, the foetus adheres to the internal skin of the matrix, and thus derives nourishment from the parent's blood, till by its weight, and augmentation of its strength, it breaks through its imprisonment, and comes perfect into the world.

As our present physicians are divided on these two systems of spermatic worms and eggs, and as all those who have lately written on generation have adopted one or the other of these opinions, it seems necessary to examine them with care, and to shew that they are not only sufficient to explain the phenomena of generation, but are also founded on suppositions void of all probability.

Another great difficulty against these two systems is, that in the egg system the first woman contained the male and female eggs: the male eggs contained only a generation of males; and that, on the contrary, the female eggs contained thousands of generations, both of males and females; insomuch that, at the same time, and in the same woman, there was always a certain number of eggs capable of developing themselves to infinity, and another number which would be unfolded but once. The same circumstance must occur in the other system, and therefore I ask if there is the smallest appearance of probability in these suppositions?

A third difficulty arises against these two systems, which is, the resemblance that children bear, sometimes to the father and sometimes to the mother, and sometimes to both; and the evident marks of extraordinary difference in mules, &c. If from the spermatic worm of the father the foetus is produced, how can the child resemble the mother; and if the foetus is pre-existing in the egg of the mother, how can the child resemble its father? or if the spermatic worm of a horse, or the egg of a she-ass contains the foetus, how can the mule participate in the nature and figure of both the horse and the ass?

These general difficulties, which are invincible, are not the only ones that can be made against these systems; there are particular ones which are no less potent. To begin with the system of spermatic worms, may it not be asked of those who admit of it, how they think this transformation is made? and object to them, that insects have not, nor cannot have any relation with what they suppose. For the worm which is to become a fly, or the caterpillar which is to become a butterfly, passes through a middle state, and when it ceases to be a chrysalis, it is completely formed and has acquired its full size, and is then in a condition of engendering; whereas in the pretended transformation of the spermatic worm into man, it cannot be said to be in a state of chrysalis, and even if we should suppose one during the first days of conception, why does not the production of this chrysalis, instead of an unformed embryo, suppose an adult and perfect being? We plainly see how analogy is here violated; and that far from confirming this idea of the transformation of the spermatic worm, it is instantly destroyed by examination.

Besides, the worm which is transformed into a fly proceeds from an egg; the egg is the produce of the copulation of the male and female, and includes the foetus, which must afterwards enter into a chrysalis, before it arrives at its state of perfection, as a fly; in which form alone it has an engendering power; whereas the spermatic worm has no faculty of generation, nor proceeds from an egg. Even should we allow the semen to contain eggs, from whence issue spermatic worms, the same difficulty will still remain, for these supposed eggs have not the copulation of the two sexes for their principle of existence, as in insects; consequently the partizans of that opinion cannot pretend any similarity, nor derive any advantage from the transformation of insects; which rather destroys the basis of their explanation.

When the innumerable multitude of spermatic worms are opposed to those physicians who are prejudiced by this system, they answer, as before observed, by the examples of plants and trees. But this comparison is not entirely just, because all the spermatic worms excepting one perish by absolute necessity, which is not the case with the seeds of a tree or plant, for those which do not become vegetables, serve as food for other organized bodies, and for the expansion and reproduction of animals; whereas we do not see any use for the spermatic worms, or any end to which we can refer their prodigious superfluity. On the whole, I only make this remark in reply to what is, or may be said on this matter; for I own, that no arguments drawn from final causes will either establish or destroy a physical system.

Another objection made against this opinion is, there being, to all appearance, an equal number of separate worms in the seed of all kinds of animals, for, say they, it is natural to imagine, that in those kinds where foetuses are most abundant, as in fishes, insects, &c. the number of spermatic worms should be more numerous than in those where generation is least abundant, as in man, quadrupeds, birds, &c. for if they are the immediate cause of production, why is there no proportion between their number and that of the foetus? Besides, there is no proportionable difference in the size of most kinds of spermatic worms, those of large animals being as small as those of the least. Those of a rat, and those of a man, are nearly the same, and when there is any difference it is no ways relative to the size of the individual. The Calmar, which is a very small fish, has spermatic worms above one hundred thousand times larger than those of a man or a dog. Another proof these worms are not the immediate and only cause of generation.

The particular difficulties that may be raised against this egg system are no less considerable. If the foetus exists in the egg before the communication of the male with the female, why do we not perceive the foetus as well in those eggs produced before as after copulation? We have before recounted the observations of Malpighius, who says he always found the foetus in those eggs produced by hens that had received the cock, and only a mass or mole in the cicatrice of those who had not; it is therefore very clear that the foetus does not exist in the egg till after impregnation.

Another difficulty against this system is, that not only the foetus is not seen in eggs before the junction of the sexes, but even the existence of eggs in viviparous animals is by no means proved. Those physicians who pretend that the spermatic worm is the foetus enveloped in a covering, are at least assured of spermatic worms; but those who affirm that the foetus is pre-existing in the egg, have no proof of the existence of the egg itself; on the contrary, there is a probability, almost equivalent to a certainty, that these eggs do not exist.

Anno 1701, page 3.

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 foetuses in the upper part, that is between the testicles and the ligature; but in the lower part there was no foetus. In the other horn of the matrix, which had not been tied by a ligature, he found three foetuses, which were regularly disposed, which proves, he says, that the foetus 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 foetus completely formed. It would only prove that the foetus 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.

Before we begin to make observations, we should have a perfect knowledge of our microscope. There is no glass whatsoever but in which there are some spots, bubbles, threads, and other defects, which should be nicely inspected, in order that such appearances should not be represented as real and unknown objects: we must also endeavour to learn what effect the imperceptible dust has which adheres to the glasses of the microscope; a perfect knowledge of which may be acquired by observing the microscope several times.

To make proper observations, the sight, or focus, of the microscope must not precisely fall on the surface of the liquor, but a little above it; as not so much reliance should be placed on what passes upon the surface, as what is seen in the body of the liquor. There are often bubbles on the surface which have irregular motions produced by the contact of the air.

We can see much better with the light of two short candles, than in the brightest day, provided this light is not agitated, which is avoided by putting a small shade on the table, inclosing the three sides of the lights and the microscope.

It will often appear as though dark and opaque bodies become transparent, and even take different colours, or form concentrical and coloured rings, or a kind of rainbow on the surface; and other matters, which are seen at first sight transparent and clouded, become black and obscure; these changes are not real, but only depend on the obliquity the sight falls on the body with, and the height of the plain in which they are found.

When there are bodies in a liquor which seem to move with great swiftness, especially when they are on the surface, they form a furrowed motion in the liquor, which appears to follow the moving body, and which we might be inclined to mistake for a tail. This appearance deceived me at first, but I clearly perceived my error, when these little bodies met others which stopped them; for there was no longer any appearance of tails. These are the remarks which occurred during my experiments, and which I submit to those who would make use of the microscope for the observation of liquors.

EXPERIMENTS.

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