*Fresh sections.*--Although these are not so satisfactory as hardened specimens for accurate histological work, it is often very useful to make them both in the post-mortem room where an immediate opinion of the nature of the tumour or diseased organ is desired, and also in the operating theatre. With a little practice sections may be cut, stained, and mounted, within ten minutes of the removal of the specimen from the body. In this way important information may be afforded to the operating surgeon, and in not a few cases it has caused the proposed treatment to be entirely altered. Thus, in one case, a supposed chronic periostitis was shown to be a sarcoma, and the limb was amputated. In another, a supposed sarcoma of the thigh was found to be a gumma, when a portion was removed and microscopically examined. A portion of the specimen should be placed without any preparation on the zinc plate of the freezing microtome, and some gum painted round it. It is then frozen. The serum in the tissues is not in sufficient mass to injure the knife when it is frozen. The knife should be wetted with, and sections transferred to, either pericardial serum, or 3/4 per cent. solution (70 grains to the pint), of common salt, neither of which causes the cells to swell up as plain water does. They should be carefully floated out on a glass slide, an operation which requires much more patience than in the case of hardened sections, as fresh sections are less coherent and also more sticky, so that the edges tend to curl up on the knife, &c. They should then be examined, one unstained, simply mounted in salt solution; another stained with picrocarmine and examined in the saline solution; and a third stained in picrocarmine, mounted in Farrant’s solution, and preserved. The last usually gives the best results, the picrocarmine staining becoming quite brilliant after a week. The glycerine, however, is apt to make the sections shrink a good deal, and the weight of the cover-glass tends to break up the unhardened section. CHAPTER IV. SECTION MOUNTING. 1. By *flotation*.