An Abstract of a Letter from Mr. Anthony Leeuwenhoeck of Delft about Generation by an Animalcule of the Male Seed. Animals in the Seed of a Frog. Some Other Observables in the Parts of a Frog. Digestion, and the Motion of the Blood in a Feavor

An Abstract of a Letter from Mr. Anthony Leeuwenhoeck of Delft about Generation by an Animalcule of the Male seed. Animals in the seed of a Frog. Some other Observables in the parts of a Frog. Digestion, and the motion of the blood in a Feavor. Having been solicitous to examine the generation of Frogs, upon the account of their young ones being like a Worm, with a round thick body and a short tail: I was surprized to find that the Male was not joined to the Female in Copulation, but that he only fate upon her; and had no Membrum Masculum: that at the same time when the Female cast her Eggs or Spawn, the Male also dropt his Seed; which is to be spread under the Eggs: in like manner as the Seed of Fishes that want the Membrum Masculum is cast under the Eggs of the Female, that the Animalia in semine may conveniently impregnate the eggs. For I hold it necessary that some one of the Animals in semine should get into a certain * point of the yolk of the egg (which point is only fit to receive it, and give it the first Nourishment, till such time as the Egg comes to be sat on) But if no one Animal should find this point, then the Egg is unfruitful: and this may be a reason why there are so many thousand more Animals in semine Masculo, than Eggs in the female. In several of my Observations I had not found the Animals taken out of the Testicles and Vasa Deferentia of Froggs to be alive. But on the first of April when Froggs were ready to spawn, I took some of the Males sitting upon the Females, and squeezed their hinder parts that I might get the seed out of the Vasa deferentia but the Ani- * By this point or speck he means the Cicatricula. malcules I then found, moved but little, because the matter they were in was full of salt particles, which made me judge it to be urine. I then cut open the Testicles and there I found an innumerable company of Animalcules swimming among a sort of ill shapen particles, these continued alive till the next day, tho there were but a small quantity of liquor to contain them. I judge the Bodies of the Animalcules to have been of the thickness of $\frac{1}{10}$ part of a hair of my head: If the matter they moved in had not been so thick I should have seen them much plainer, nevertheless they are represented to the best of my skill in Fig. first where A B C is an Animalcule as it lay in the Watry matter, and moved itself therein, sometimes the head appeared to be thicker than other times, and often I could see the Body but from A to B by reason of the thinness of the Tail BC. when the Animal moved itself strongly, tho the progress were but little, the motion towards the head was like that of a Snake, and the tail was cast into 3 or 4 Bows. Fig. D is an Animalcule lying dead, and stretcht out at length, but in this posture I saw but few, for many that were dead lay with the fore part of their body bent in, as in Fig. E others made as it were a half circle others had the forepart of their Body bent and moved their hinder parts: these last I took to be ready to dye. The number of Animalcules in all the seed was so great that I judge there might be 10000 of them to one of the Females Eggs, the same computation I formerly made of the Milt of a Codfish, but it must not be thought that all the Animals in the Milt of the Codfish live together, but only such of them as are nearest the passage they are to be cast out of, and who have more moisture about them; the rest of them being more remote in the body, and being encompassed with a thicker matter, are not alive; for the some fishes, as the Breame, and Trout, cast their Milt and Spawn in two days time, yet Codfishes are about a Moneth in in doing it; in all which time the seed is successively ripened and perfected. So also are Froggs by what I have experienced, for the first Animals I fought were dead, and though I afterwards found live ones, yet those were dead that lay deepest in the Testicle. 'Tis well known that when a Cock hath trod a Hen but once, many Eggs are made fruitful, the reason that I give for it is, that many of the Eggs in the Ovary, have each of them received an Animalcule out of the Male seed. This Animalcule while the Egg is late upon does not presently take the figure of a Chick, but grows into a disorderly Bulk, wherein the heart is first plainly to be discerned. Other Fetus's have a different way of growth, the Louse has all its parts, and is a Breeder while it is yet in the Egg; the Flea shows like globules swimming in a watry substance, it afterwards becomes a Worm, then a Nympa. The Frog is a thick Worm till it be of a considerable bigness. The Humane Fetus tho no bigger than a Green Pea, yet is furnished with all its parts. I have often endeavoured to discover the Animal coming out of the Male seed, in the egg of the Hen; but have been unsuccessful tho some of the Globules of the Egg were magnified to the bigness of common Apples. This disappointment has put me upon the Eggs of Insects as the Flea, and Louse, which being very small, may be so much the fitter for this discovery. A certain Physician writing of Generation sets down these words, in the Margent from the female seed the fruit must grow however the thing came to pass. This he enlarges upon in the Text, but I think under correction that by one instance I shall bring a sufficient proof of the fruits coming from the Male seed, and the females only contributing to the nourishment and growth of it. Many of our Neighbours either for their pleasure or profit, keep tame Rabbits, which are large long eard, ordinarily of a white colour, but sometimes of a Blew, Black, and Pyed; those that would make a profit of these Rabbets by causing them to bring gray young ones, which in the fore part of the year may be sold for a wild kind; get a grey Male, such as are ordinarily found on our sand hills, to put to their female. The Breed that comes from hence always takes the gray colour of the Male, and it has never been seen that any of the young has had any white, or other coloured hair then gray, there withal they are never so bigg as the Dam, nor have so great ears, nor are so tame, but of a wilder kind. The first Frog which I anatomized lay on the ground in my way, and seemed so weak through cold that tho I kicked it with my foot, it would not leap away, this proved a Female; in the guts of it I found worms like those in Children of about the thickness of a hair of my head. The blood consisted of flat oval particles, swimming in a clear liquor: these had no colour as they lay singly, but when 2 of them lay upon one another, as here Fig. 2d. their colour was stronger. A is an Ovale of blood partly covered with B a 2d. Ovale of blood, C is a 3d. Ovale of blood covering a part of ACB as at D. and casting a deeper colour, by reason that 3 Plates lie upon one another: But there was another small Oval hard by represented by E which showed of a higher red than the three Plates together. Many of these Ovale particles were very pleasant to look upon, especially when the moisture wherein they swam (having also Globules on the surface as big as 1/6 of a blood Globule) was evaporated; for some had in the middle a faint Ovale shade, others appeared as if they were made of several Ovales of unequal bigness, others seemed to be set round with small globules, others had no globules in the Circumference, but several in the middle: these Globules I believe were at first swimming in the Watry liquor under the Ovales, tho now they cleave to them by Accident. Upon the Plate whereon I layed the Frog that I anatomized I found several Animals moving in a watry blood, they were about half as long and half as broad as the Oval Particles, and about 50 of them might lie in the space of of a sand, these I had never seen in the pure blood, nor could I perceive them in the water that came out upon ripping the skin from the flesh, or upon opening the belly, or squeezing the head of the Frog to make it lie quiet upon the Plate. At length in the month of June I met with some froggs whose excrement was full of an innumerable company of living Creatures, of different sorts and sizes, the greatest sort were shaped like Fig. F and of these I judged that 40 might be in the space of a sand. The 2d sort had the shape of Fig. G. there were but few in number. The 3d sort was like our River Eels as Fig. H. and these were more in number than the first; But the whole excrement besides was so full of living things, that it seemed all to move, & I guess there was not less than 1000 of the third sort in the space of a sand. From hence I concluded that the Animals found among the blood might come from my cutting a Gut. By the way I observed something of the damage that froggs may do to fish-ponds, for I took out of some of their Stomachs 8. 10 or more young fishes. I took notice of a small vein, of about the thickness of a hair of my head, that when the blood was out of it, the Coat was like a frog's outward skin. The same Coat of the vein was made of threads or filaments running by the side of one another, just as if they had been wound close about a small round stick, so as to cover it all over. Now if there be Capillarys in the body a 1000 times less than this which I examined, how thin must the threads necessarily be of which the Coat is made? and how easily must these threads be separated and divided from one another, so as to let the blood when it is very forcibly moved in the Arterys, start out between them; and I was the more confirmed in this Opinion, upon spreading hard the Coat of the vein, for I then saw through it as through a hair fine, hence may a probable account be given of St. Anthonys fire, red swellings, or the Small pocks, and perhaps the blood may be more gently strained through these passages for the nourishing of some parts of the body. I examined one of the Muscles of the hinder leg of a frog, which consisted of filaments, and those again of a great number of lesser filaments, but because they had more rings in them than I had formerly seen in the muscular threds of an Oxe, Fly, Gnat, Flea or Louse, I have here represented part of one in Fig. I. Such numerous rings I have since met with in the filaments of the Muscle of a Lamb, taken from the rim of the Belly, near the hinder leg. From the indentings of these filaments I cannot only satisfy myself how the limbs come to stand bent, when the muscles are at rest, but also why we can walk a longer time than stand still; and why our Arms when we walk do not hang down at their full length, stretch out by our sides; but more backwards and forwards; for if the Arms should still hang straight down, then would one Muscle be stretcht too much, and another bent or drawn up too close; both these things disagreeing with the Natural constitution of the Muscle, and for this reason it is, that when we stand a long time, we do not rest equally upon both legs, but first raise up one foot, then the other, touching the ground only with the fore part of the foot, while the Muscles of that leg rest themselves. I have been puzzled why some of the wrinles in the filaments of Flesh and Fish muscles, were serpentine, as I represented in my letter of the 3d. of March (Fig. 1st. E E G H and I K L M.) but I consider that the filaments lose their roundness by being prest hard upon one another. It is also probable that they may be bent after that manner by the evaporating of their moisture, which makes up $\frac{2}{3}$ parts of their bulk: as Fig. K. $\alpha \beta \gamma \delta.$ is a Filament which had been round, but is now altered by the evaporating of its moisture, and bended in as at $\omega,$ where- by the rings that were formerly straight; appear serpentine, as between β and γ. In a letter of mine to Mr. Oldenburg (which was not published) I affirmed, that Concoction was not performed by an Acidliquor dissolving our meat, but by the motion of the Stomach, and guts, which bruises, and breaks the meat to pieces. This motion is caused by the Diaphragme pressing upon the parts of the lower belly, as often as we take breath; in the same manner as a bladder almost full of water, is molded and rolled between the hands. There is also a natural warmth to be considered in the stomach, and a natural folding or closing itself, about the Vitalis which it holds, be it never so little; but especially there is a kneading or contracting of themselves, remarkable in the Bowels of beasts, even after they are taken out of the body. I am lately more confirmed in this opinion, by my observations on the Excrements of a Codfish, which I find to be made up of very short pieces of the Filaments of Fish, appearing by the Microscope like the shavings of ones Beard, for as in some Creatures the taking of breath, so in fishes the moving of the Gills, causes a compression and dilatation in the stomach, whereby the Aliment is catcht in its folds, nipt a sunder, and divided into such small particles as are fit for the nourishment of their bodies. Now if the Contraction of the stomach be supposed to happen no oftner then a man breaths in an hour, there will be about 3000 times: which will be quickly enough to waft, and tear in pieces a little fish swallowed down by a great one, although the teeth of the Devourer, and the Acidjuice should contribute nothing to digestion. Sometimes these threds are not to be found in the excrements, as perhaps when the Codfish has been long catcht; and without food, for then the threds are broken so short; that they are no bigger when they are voyded, then small Globules, which I judged to be of a blood Globule. When the Codfish has abundance of food, then the pieces of threds are driven the faster out of the stomach, and through the Bowels, and therefore are the less broken and shortened. Such like Filaments or pieces of flesh I have observed in my own Excrements, which I conceive were made by the nipping of the folds of the stomach: for these Filaments are not strong, when there lie yet few of them together; or when we make a Cord or Rope of them, which upon stretching bears unequally; though in another case a muscle made up of several of these filaments, and bearing equally in every part, may be very strong. I have often maintained among our Physicians, that tho the heart and Pulse beat quicker than ordinary, yet the Circulation of the blood is not performed in lesser time; and the reasons which I gave were these. The blood in many Feavorish persons is very thick, and therefore passes slowly, and with difficulty, thro the smaller Arterys, and requires a very strong beating in the heart to force its way. When the blood is thick and makes this resistance, the heart upon contracting itself, cannot force it all out, but a great part remains behind in the Ventricles. This remaining blood being over heated by the heart, makes that little blood which comes fresh out of the Veins, too hot likewise; and in the mean time the heart not being able to free itself of all the blood contained in its Cavities, casts out only the thinner part, which is quickly spent in the nourishment of the body, whereby the blood still becomes thicker, and circulates less fast. I can not admit that the time of the circuit of the blood, should be estimated by the number of Pulses in an hour, and the capacity of the Cavitys of the heart; for as the Lungs upon expiration are never totally without air, so the heart in a well constituted body, is never upon the Systole absolutely without blood: I imagine also that when the heart is too full of blood (as I have before urged) its muscles may be so far strained, and kept beyond their usual bent, that they they would not be relaxed, tho' the blood were very thin, and fit for motion; just as we see the bladder by being kept long too full of water, has the Muscles so reacht, that they can not be contracted. So also the Eastern People who would acquire to themselves the reputation of Saints, remain with their Limbs so long stretcht out in one posture, that they can not draw them back again.