There is, perhaps, no trade which is more destructive of human life than that of the fork-grinder was until the peculiar respirator was made obligatory. The minute particles of steel thrown off by the grindstone fill the air, and were necessarily inhaled. Now, the human lungs are capable of enduring very bad treatment, but the introduction of steel-dust into them is more than they can bear. Consequently the duration of human life was very short, consumption almost invariably setting in at an early age, and carrying off the men before they had achieved middle age. Nor did the mischief end there. It was bad enough that life should be shortened, but far worse that it should be wasted, as was mostly the case. The men, knowing what their fate must be, were simply reckless, and plunged into all kinds of debauchery, under the plea of “a short life and a merry one.” They knew no better, and could scarcely be blamed for their mode of living. And, as a matter of course, each succeeding generation was worse, smaller, and feebler than the preceding. Then there came the invention of the Magnetic Respirator, by which the fork-grinder’s trade was rendered as healthy as any other. It was made of steel-wire gauze, and magnetised, so that the floating particles of steel were not only stopped in their progress to the lungs, but arrested by the magnetism, and, so to speak, taken prisoners by it. Even a well-made respirator of several layers, like those which are used by persons suffering from weak lungs, would have been useful, but the addition of magnetism doubled the efficacy while greatly diminishing the cost, a single layer of wire being quite adequate to the office, and was, in fact, quite a stroke of genius. The value of this invention is at once shown by the many complaints which the workmen made when the Respirator was first introduced. They complained that the apertures of the Respirator became so choked that they could not breathe. This was perfectly true, but the complaint showed the real value of the instrument. [Illustration: SPIRACLE OF FLY.] [Illustration: RESPIRATOR OF FORK-GRINDER.] It was necessary for the workmen, every now and then, to clear off the innumerable particles of steel which adhered to the magnetised wires, and impeded respiration. But they never seemed to realise the fact that, if it had not been for these wires, all the particles would have been drawn into the lungs, and gradually choked them up, brought on inflammation, and extinguished their life altogether. And, with the usual repugnance to new ideas which is inherent in undeveloped minds, the men stoutly resisted the introduction of the Respirator, and did their best to reject an invention which doubled the length of their lives, and enabled them to find long happiness in the world instead of brief pleasure ended by sure and painful death. * * * * * NOW, we will see how the principle of the Respirator is carried out in Nature.