the glycerine jelly by first passing the blade of a knife, held in a vertical position, the back of the knife being next to the slide, around the edge of the cover glass. After turning the knife-blade so that the flat side is in contact with slide, remove the jelly outside of the cover glass. Any remaining fragments should be removed with a piece of old linen or cotton cloth. Finally, ring the edge of the cover glass with microscopical cement, of which there are many types to be had. If the cleaning has been done thoroughly, there is no better ringing cement than Canada balsam. In mounting cross-sections, the method of procedure is similar to the above, with the exception that the glycerine jelly is placed at the side of the specimen and not in the centre. While melting the jelly, incline the slide in order to allow the melted glycerine jelly to flow gradually over the specimen, thus replacing the air contained in the cells and intercellular spaces. Finish the mounting as directed above, but under no conditions should you stir the glycerine jelly with the section. If specimens, after having been embedded in paraffin or collodion, are cut, cleared, stained, and dehydrated, they are usually mounted in Canada balsam. A small drop of this substance, which may be obtained in collapsible tubes, is placed at one side of the specimen. While inclining the slide, gently heat until the Canada balsam covers the specimen. Secure a cover glass by the aid of pliers, pass it through the flame three times, and lower it slowly while holding it in an inclined position. Press gently on the cover glass with the needle-handle, and keep in a horizontal position for twenty-four hours, then place directly in a slide box or cabinet, since no sealing is required. Glycerine is sometimes used to make permanent mounts, but it is unsatisfactory, because the cover glass is easily removed and the specimen spoiled or lost, unless ringed--a procedure which is not easily accomplished. If the specimen is to be mounted in glycerine, it must first be placed in a mixture of alcohol, glycerine, and water, and then transferred to glycerine. Lactic acid is another permanent liquid-mounting medium, which is unsatisfactory in the same way as glycerine, but like glycerine, there are certain special cases where it is desirable to use it. When this is used, the slides should be kept in a horizontal position, unless ringed. COVER GLASSES Great care should be used In the selection of =cover glasses=, however, not only as regards their shape but as to their thickness. The standard tube length of the different manufacturers makes an allowance of a definite thickness for cover glasses. It is necessary, therefore, to use cover glasses made by the manufacturer of the microscope in use.