When fresh from the dealer’s hands, these slides are generally covered with dust, &c., which may be removed by well washing in clean rain-water; but if the impurity is obstinate, a little washing soda may be added, care being taken, however, that every trace of this is removed by subsequent waters, otherwise the crystals will afterwards form upon the surface. A clean linen cloth should be used to dry the slides, after which they may be laid by for use. Immediately, however, before being used for the reception of objects by any of the following processes, all dust must be removed by rubbing the surface with clean wash-leather or a piece of cambric, and, _if needful_, breathing upon it, and then using the leather or cambric until perfectly dry. Any small particles left upon the surface may generally be removed by blowing gently upon it, taking care to allow no damp to remain. We have before said, that any object to be viewed in the microscope must have its support; but if this object is to be preserved, care must be taken that it is defended from the dust and other impurities. For this purpose it is necessary to use some transparent cover, the most usual at one time being a plate of mica, on account of its thinness; this substance is now, however, never used, thin glass being substituted, which answers admirably. Sometimes it is required to “_take up_” as little space as possible, owing to the shortness of focus of the object-glasses. It can be procured of any thickness, from one-fiftieth to one-two-hundred-and-fiftieth of an inch. On account of its want of strength it is difficult to cut, as it is very liable to “_fly_” from the point of the diamond. To overcome this tendency as much as possible, it must be laid upon a thicker piece, previously made wet with water, which causes the thin glass to adhere more firmly, and consequently to bear the pressure required in cutting the covers. The process of cutting being so difficult, especially with the thinner kinds, little or nothing is gained by cutting those which can be got from the dealers, as the loss and breakage is necessarily greater in the hands of an amateur. It is convenient, however, to have on hand a few larger pieces, from which unusual sizes may be cut when required.