12. _Employment of Microtome._—The paraffine being sufficiently hard, we will clamp the microtome on to the table, and seat ourselves on a chair of convenient height before it. To our right stand the basin of water, razor, and section-knife; the beaker of spirit to the left, and a cloth on our knee. A few turns of the microtome screw having brought the paraffine to the surface, a thick slice is to be cut off, and this repeated until the imbedded tissue comes into view. This preliminary work had best be done with the razor, as it is needless to subject our section-knife to unnecessary wear and tear. By a fractional revolution of the screw the tissue is now slightly elevated, and with the pipette held in the left hand, a large drop of spirit is to be let fall upon its surface. The section-knife, grasped firmly but lightly in the right hand, is to be laid flat upon the cutting-plate of the machine, so as to occupy the diagonal position shown in the figure. Two fingers of the left hand are now laid gently upon the back of the blade, so as to give it an equable support, whilst the knife with a rapid motion is pushed in the combined direction of _forwards_ and to the _left_, so that the blade in cutting the tissue will pass through it from point to heel. Thus it will be observed that the stroke of the knife is _from_ the operator—a far easier and more effective mode of cutting than the reverse plan. The blade of the knife, having the section just cut, either floating in a small pool of spirit on its surface or adhering thereto, must now be immersed in the basin of water, when by a little very gentle agitation of the knife the section will be floated off. And now we shall find the great practical value of immersing the tissue in gum before imbedding, for no sooner is the section disengaged from the knife than the thin film of gum which separates the paraffine from it becomes dissolved, and the section will be observed gradually to subside to the bottom, leaving the paraffine floating upon the surface. After carefully wiping the knife from all shreds of paraffine, the microtome screw must again be partially revolved, more spirit applied to the tissue, and another section being cut, it must be transferred to the water as before, and so on, until a sufficient number of sections have been obtained. As to how thin the sections should be cut, no general directions can be given; each case must be regulated by its own conditions. The denser the tissue, the thinner should the section be; whilst certain substances of loose and spongy texture do not require the sections to be particularly thin—it may be said, however, in a general way that sections, and especially animal ones, _cannot be cut too thin_ so long as they remain perfect and entire. If Professor Rutherford’s microtome (as made by Gardner) be employed, the head of the screw will be found to be graduated into divisions of slightly unequal value; the