Some authors, in support of a favourite system, have made bold assertions on the subject of animalcula; the small-pox, the measles, the epilepsy, &c. have been attributed to them: Langius reduces all diseases in general to the same principle. A writer at Paris, who assumed the title of an English physician, has proceeded still farther; he not only accounts for all diseases, but for the operation of all medicines, from the hypothesis of animalcula. He has peculiar animals for every disorder; scorbutic animalcula, podagrical animalcula, variolous animalcula, &c. all at his service. Journ. des Scav. tom. lxxxvii. p. 535, &c.
It is not at all surprising that the wonderful discoveries relating to animalcula should have been applied, however improperly, to support the most whimsical and chymerical systems. Most of the discoveries in natural philosophy have been subjected to similar abuses, and laid the foundation for the warm imaginations of some men to fabricate visionary theories; these have been of great prejudice to real science, the primary object and ultimate reward of which is the acquisition of truth. Edit.
The animalcula of this, and the first species are so numerous as to exceed all calculation, though they are contained in a very confined space.
6. Monas Mica.
M. circulo notata. Mona, marked with a circle.
This lucid little point may be discovered with the third lens of the common single microscope; when the magnifying power is increased, it appears either of an oval or spherical figure, for it assumes each of these at pleasure. It is transparent, and has a small ellipse inscribed as it were within its circumference; this ellipse is moveable, being sometimes in the middle, sometimes a little towards the fore-part, at others, nearer the hind-part. There is a considerable variety in its motions; it often turns round for a long time in the same place; an appearance like two kidneys may sometimes be perceived in the middle of the body, and the animalculum is beautifully encompassed with a kind of halo, arising most probably from invisible and vibrating fibrillæ. They are to be found in the purest waters.
7. Monas Tranquilla.
M. ovata, hyalina, margine nigro. Egg-shaped, transparent mona, with a black margin.
These animated points seem to be nearly fixed to one spot, where they have a fluctuating or reeling motion. They are frequently surrounded with a halo, and differ in their figure, being sometimes rather spherical, at others quadrangular. The black margin is not always to be found, and sometimes one would almost be tempted to think it had a tail. They are found in urine which has been kept for a time. The urine is covered, after it has remained in the vessel, with a dark-coloured pellicle or film, in which these animals live: although the urine was preserved for several months, no new animalcula were observed therein. It has been already shewn, that a drop of urine is in general fatal to other animalcula, yet we find in this instance, that there are animated beings of a peculiar kind, appropriated to, and living in it.