The top of the cover-glass should always be perfectly dry; and if by any chance the objective becomes wet it should be wiped perfectly dry with a piece of old silk or with chamois leather. Also, if permanent mounting is attempted, and the preservative liquid is allowed to come in contact with the objective, such liquid must, of course, be washed off with some suitable solvent before any attempt is made to wipe the lens dry. If the object under examination is of such dimensions that the cover-glass has a tendency to rock on it, or if it is a living object of such a size that it is unable to move freely in the exceedingly thin film of water between the cover and the slip, it should be placed in a cell. The cell may be made by cementing a ring of glass or vulcanite to the middle of a slip, or it may be a little circular cavity prepared in the slip itself. In either case the cell must be quite full of water before the cover-glass is applied, so that no air-bubbles are included. Hitherto we have spoken only of mounting small objects in water, and this is advisable when the object is moist, whether it be animal or vegetable, alive or dead. But dry objects may be examined in the dry state, in which case they need not be covered. If they are composed of transparent material they are to be dealt with in the manner recommended before, as far as the management of the light is considered; that is, a moderately strong light is sent through them by the reflector below the stage; but opaque objects are best examined on a dead black ground, the light being directed on to them by means of a condensing lens placed between them and the source of light. A collector who has done only a few days’ work on the sea shore will probably find himself the possessor of a host of interesting objects that will afford much pleasure and instruction when placed under the microscope--objects, many of which have been somewhat hastily deposited in a bottle of spirit or other preservative for study in his future leisure moments. These objects, if small, may be examined as above described, simply placing them under a cover-glass, or in a cell, with a clear drop of the same liquid in which they have been kept. The general characters of the larger objects may also be observed by means of some kind of hand lens, but even these are generally best examined under water or other suitable liquid. A great deal may be learnt of natural objects by preparing very thin sections for microscopic examination; and although special works should be consulted if one desires to become proficient in the different methods of cutting and preparing such sections, yet a great amount of good work may be done with the aid of a sharp razor, manipulated with nothing more than ordinary skill.