VOL. XLIX.] VHILOSOPHICAL TRANSACTIONS. 6qQ 



May 1, 1752, at 11 o clock forenoon, Mr. W. made an infusion of dried 

 millepedes, or wood-lice, such as are commonly kept in the apothecaries' shops. 

 These he put unhruised into a small phial, so as to make it half full; then poured 

 on them as much boiling water as filled it neck and all, stopped it with a well 

 masticated cork, and put it into a pocket, where it was kept in a mild degree of 

 warmth. He let it remain till 10 o'clock the same evening, when he examined 

 a drop of the infusion with the highest magnifier of a very good microscope 

 made by Mr. Clarke of Edinburgh. He found the whole swarming with oblong, 

 slender, flatfish pellucid animalcules, pretty nearly of the same breadth through- 

 out the whole length of their bodies, and without any appearance of a tail, fig. 

 13, pi. 16, all evidently of the same kind, though not all of the same length 

 and^dimensions, extremely vivid, and, as appeared, spontaneous in their motions, 

 which they performed in all directions in an undulatory, vermicular way. 



Observing the speedy appearance of these animalcules, he wished to know, in 

 how short a time they might be produced; for which pui-pose. May 3d, he made 

 just such another infusion, putting it into his pocket, as before, and an hour 

 afterwards laid a drop of it before the microscope, while it was as yet milk warm. 

 He observed a very few of these minute bodies moving about briskly in the fluid. 

 An hour after this more of them appeared ; and before the end of the 3d hour, 

 the infusion contained a great number of them. They continued however to 

 increase in numbers for an hour or two afterwards, when the infusion seemed to 

 have produced all that it was capable of. 



June 3d, he made an infusion in the same way of unbruised cantharides, and in 

 much about the same time found the whole swarming with animalcules of the 

 same kind as those of the infusion of millepedes. These bodies, which at first 

 appeared larger than those in semine masculino, were very soon decomposed into 

 smaller ones, to speak according to the doctrine of Messrs. Needham and BufFon, 

 or, as others would rather incline to express it, succeeded by smaller ones, these 

 again by others still smaller, and so on, until in a few days, the highest magni- 

 fier of the microscope could exhibit nothing distinct to the eye. The same sub- 

 stances infused in rectified spirits of wine, or other spirits, showed none of 

 these bodies; and a few drops of such liquors, or of a solution of fixed or volatile 

 alkaline salts, poured into the infusions, instantly destroyed the animalcules. 



Mr. W. declines inquiring, whether these animalcules are produced by the 

 decomposition of the substances in which we observe them, which, according to 

 Mons. de BufFon contain a number of living organic particles, or, according to 

 Mr. Needham, a vegetating force in every microscopical point, capable of form- 

 ing secondary combinations, microscopical plants, zoophytes or animalcules, 

 according to the greater or less degree of exaltation, which the several substances 

 have attained. Or whether they proceed from ova formerly existing in the sub- 



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