[Q] See New Discoveries made with the microscope by Mr. Needham, chap. vi. Leyden, 1747. "When the small machines, he says, are arrived to their perfect maturity, many of them act the moment they are in the open air; nevertheless most of them may be commodiously placed, so as to be seen with a microscope, before their action begins; and even to make them act, the upper extremity of the external case must be moistened with a drop of water which then begins to expand, while the two small ligaments which issue from the case twist and turn in different manners: at the same time, the screw ascends slowly, the volutes, which are at its upper end, approach and act against the top of the case: those at the bottom also advance, and seem to be continually followed by others which come from the piston. I say, they seem to be followed, because I do not think they are so effectually, but only a deception produced by the nature and motion of the screw. The piston and barrel also follow the same direction, extend lengthways, and at the same time move towards the top of the case, which is perceived by the vacuum at the bottom. As soon as the screw, with the tube in which it is enclosed, begins to appear externally from the case, it folds, because it is retained by its two ligaments: nevertheless, all the internal contents continue to move gently and gradually, until the screw, piston, and bladder, are entirely come out. When that is done, the rest follow directly after. The piston separates from the barrel, and the apparent ligament, which is below the latter, swells and acquires a diameter equal to that of the spongy substance which follows it. This, although much larger than when in the case, becomes still five times longer than before. The tube which incloses it all is straightened in its middle, and forms two kinds of knots, about a third of its length distant from each extremity: the semen then flows through, and is composed of small opaque globules, which float in a serous matter, without shewing any signs of life, and which are precisely such as I have said to have seen them when they were diffused in the reservoir of the milt. In the figure, the part between the two knots seems to be broken: when it is examined attentively, we find that what causes it to appear as such, is, that the spongy substance with in the tube is broken in nearly equal pieces, which the following phenomena will clearly prove. Sometimes it happens, that the screw and the tube break by the piston, which remains in the barrel; then the tube closes in a moment, and takes a conical figure, by contracting, as much as it is possible, above the end of the screw, which demonstrates its great elasticity in that part: and the manner in which it accommodates itself with the figure of the substance it incloses, when it receives the least change, proves, that it is equal in every other respect."