Cutting instruments act in two ways—either as simple wedges or as a series of wedges, the latter being generally known as the saw-like action. It is frequently stated in school philosophies that the edges of _all_ cutting instruments are toothed like a saw, and that they act like a saw; this is evidently not the case with many, such as the axe, the chisel, the plane, etc., and it is not even true of several to which it is frequently applied, such as the razor, the penknife, etc. The action can be said to be “saw-like” only when the teeth act as independent wedges and remove a small portion of the substance acted upon, the portion being known as _saw-dust_. Now in cutting sections of wood with a sharp razor, where but a single stroke is used to carry the cutting edge across a section, say half an inch in diameter, the edge of the razor does not act like a saw; none of the material is removed except the section itself; in other words, there is no saw-dust. That the edge of the knife or razor is not even, is very easily proved by means of the microscope, but it will be found that the notches and projections form a series of lancet-shaped knifelets, each one of which acts just as does the blade of a penknife when drawn over a piece of wood or a quire of paper. Now if we lay a quire of paper on a board and draw the edge of a penknife over it, we will cut down through the paper, not by sawing but by a moving wedge. It is precisely in this way that the little lancet-shaped teeth on the edge of a razor act when the latter is used to cut a section. If we further examine the edge of the razor, we will find that the bottoms of the notches are comparatively blunt; if therefore we press the razor directly forward we soon press these blunt portions of the general edge against the material to be cut, and the resistance becomes so great that the material is actually crushed or torn. This would not happen if we had an absolutely perfect edge—one without any notches. This being practically unattainable, however, we must endeavor to make up for it by a sawing motion, (though not a sawing action) at the same time seeking to avoid as much as possible those saw-like features which render this motion necessary. We have dwelt at length upon this point because so much has been written comparing the edge of a razor to that of a saw, that some persons actually advise us to give the edges of our knives and razors a saw-like character, under the impression that by so doing they will work better. This is a fallacy; the best work will be obtained from the smoothest and most perfect edge, provided the latter is thin enough.