It has proved a matter of extreme difficulty to inves tigate the nature of these animals. Their wonderful minuteness has called their very existence into doubt. None but the most experienced observers have been able to discern them; and the tail, which is almost a universal characteristic, could be seen even by them, only when in a certain position. Leeuwenhoek and Hartsoeker both claim the discovery of seminal vermi culi; Haller ascribes it to Ludovic Hamma, a young German.
On presenting the fluid taken warm from an animal, to a powerful magnifier, infinite numbers of vermiculi are observed swimming with very lively motion, and varying their course as fishes do in water. Their gene ral figure resembles that of a tadpole, excepting that the tail is longer in proportion, and the body of smaller dimensions. If the portion taken for examination is of too thick consistency, it may be diluted with saliva, which is the only transparent liquid not fatal to the ver miculi; they then become clearly and distinctly visible, smaller than the red globules of blood. The human fluid being taken from a dead body, and presented to the microscope, the thermometer standing at 48°, no thing could at first be discovered, on account of its opa city. When beginning to dissolve, the irregular parts seemed in an indistinct slow fermentation; but, on en creasing the magnifying power, the motion was seen to arise from corpuscula infinitely more minute than these parts, of a globular figure, and provided with a short filament, or tail. These were the vermiculi, which ex hibited two kinds of motion, one consisting merely in oscillation from right to left, and the other in progres sion forward. But they seemed insensible of the sur rounding objects, and blindly rushed against them; or, if involved amidst a number of obstacles, they pushed their way through the places where they found no re sistance. In twenty-three minutes, their motion, which had been incessant„began to decline, and in an hour and a half it was almost totally gone.
The fluid of a ram being put in a watch-glass, it ap peared to the naked eye in continual agitation, though situated on an immoveable plane. On examination with the microscope, this was observed to proceed from in numerable vermiculi all in motion, which wege larger than the former : the body, an oval part, sometimes was immersed in the fluid, or disappeared, and sometimes came to the surface. Though the thermometer was at they hardly live an hour.
Similar vermicul re found in the prolific fluid of all male animals, from those of the largest size down to the smallest insect; and naturalists affirm, that a gene ral resemblance pervades the whole ; as the chief dif ference, except in a few examples, consists in the length and slenderness of the tail. But the size bf the vermi culi does not depend on that of the animal, for they are found larger in the small ones, than in some of greater bulk : neither are they all of equal size among them selves, which is particularly evident in the fluid of the horse.
The vermiculi of the water newt have a singular tail ; it is of immoderate length, compared with the rest of the body, and along each side is a row of minute points, or hairs, moving like oars, and thus aiding the swim ming of the animal. The vermiculi of the frog do not exhibit the distinct and peculiar tail by which the rest are commonly distinguished; but as some vermiculi seem to possess the power of changing their appear ance, it is possible that the observer may have occa sionally been deceived.
The period that these animals survive in the open air is various. Those of mankind do not live above seven or eight hours : but, enclosed in glass tubes, they live two days during summer, and in spring or autumn al most three. Leeuwenhock preserved those of a seven days, and a few of them then swain with as much velocity, as if they had come recently from the animal. The earlier death of the human vermiculi during sum mer, is supposed to arise from some noxious quality imparted to the fluid from the atmosphere, which per haps consists in incipient putrescence. They have lived two days and a half when the heat of the atmosphere was 63°,• but kept at about 97°, they died in less than fourteen hours. Baron Gleichen could not keep those of the horse alive above two hours. The heat of 131° is fatal to the human vermiculi; those of the horse and dog perish at 126°, and those of the bull at 133°. Sun shine, at a much inferior degree, is fatal to them in open vessels, though not if they are enclosed in tubes. Cold is also destructive of vermiculi, but some are more robust than others. It first reduces them to a lethargic state, from which they may be aroused by the applica tion of heat: if the cold is too intense they die. Those of the bull can support 27° below the freezing point without dying; and their vivacity continues three or four hours, where the cold equals that of freezing.