INTRODUCTIONWhen mounting sections on a slide, it is essential that the slide be ultraclean. To ensure that the section sticks to the slide, slides can be covered with a thin layer of gelatin. The process of cleaning and gelatin-coating is called “subbing.” Several boxes of slides should be subbed at a time and stored, covered, in the refrigerator until they are needed. Subbed slides can also be purchased commercially.