obtained by especial care in imbedding, using graded paraffins and finally imbedding in a 56°C. paraffin. The pieces of tissue should be small, and the sections may be cut with a knife wet with water or alcohol. _Serial paraffin sections_ are easily obtained; in fact, paraffin imbedding is by far the best method for serial cutting. To cut ribbons of sections upon the ordinary slide microtome the block must be clamped into the object-holder so that the edge of the block facing the knife, as well as the opposite side of the block, is parallel with the knife-edge. The knife should be placed at right angles to the microtome. If the paraffin has the right consistency the edges of the sections as they are cut will adhere, and a ribbon of serial sections will be pushed up over the knife. This ribbon can be cut into pieces of the desired length and mounted according to the directions given in the next chapter. The Minot automatic rotary microtome is especially well adapted for the cutting of ribbon sections. Failure of sections to adhere to each other is usually the result of too hard consistence of the paraffin, and this can be remedied by warming slightly, according to the method given above. If the paraffin is too soft the sections fold together. The block may be cooled in ice-water, or the sections may be cut with a cooled knife. Paraffin knives so constructed that they may be cooled by a stream of ice-water are supplied by dealers in microtomes. The conditions essential for successful paraffin cutting are perfect infiltration and imbedding, sharp clean knives and a certain degree of skill in manipulation that can only be secured by practice. CHAPTER XXIV. THE PREPARATION OF MOUNTED SECTIONS. Sections of fresh material, unimbedded or imbedded tissues must be treated by a series of processes before they are finally permanently mounted and ready for use. These processes in general are: =preparation for staining=, =staining=, =differentiation=, =washing=, =dehydration=, =clearing= and =mounting=. The general procedure will be modified to some extent by the character of the tissue, manner of preparation (fixed or unfixed, imbedded or unimbedded, unstained or stained), character of stain (affected by alcohol, xylol, etc.), and the mounting agent (glycerin, balsam, damar, colophonium). Two or more of these steps may be combined in one; the same agent may differentiate, dehydrate and clear. Several stains may be combined in one solution, or it may be necessary to use them in succession. The very greatest variation is possible in pathologic technique; in fact, practically every laboratory worker modifies methods according to the light of his individual experience. The really important thing is to be master of the method, and not allow the method to control the situation. One of the greatest attractions about laboratory work is the infinite possibility of variation and improvement of methods and the invention of new ones.