A STILL better system is where the section-knife is held in a frame which slides on the plate so that the edge is kept just above the surface. In this way the edge of the knife is never dulled by grinding on glass or metal. A common mistake in this form, however, is to raise the cutting edge too far above the surface of the plate. This gives rise to great irregularities. NOTE F., Page 22. AS the size of the sections which it may be desired to cut, varies within wide limits, the best microtomes made in this country are furnished with as many as three tubes or “bushings,” fitting one within the other, and in this way the hole may be partially filled up and thus reduced in size. This enables us to obtain a range of from one inch and a quarter, suitable for large histological preparations, to one-eighth of an inch for such objects as hair sections. NOTE G., Page 37. KNIVES FOR CUTTING SECTIONS. SUCCESS in cutting sections depends more upon the excellence of the knife that is used than upon any other one point, and therefore the art of keeping the knife in good order is one which should be acquired by every microscopist, even at the cost of considerable time, study and labor. As a stepping stone to the acquisition of this art, there are certain general principles which must be thoroughly understood before we can hope for success in practice. These principles are simple, and when once clearly stated, quite obvious, but they are frequently overlooked.