MAKING SECTIONS 69 



be noted briefly. Some people neither drain the water from the sHde nor heat 

 the slide over the lamp but merely place it, as soon as the water has been 

 added to it, on the thermostatically controlled hot plate. This permits the 

 sections to dry and to flatten at the same time. The objection to this procedure 

 is that contained air in the water used for flattening almost invariably comes 

 out in the form of bubbles, which accumulate under the sections, either caus- 

 ing them to fall off or at least making it very difficult to observe properly 

 when mounted. There is also the risk in this procedure that the water will 

 not stop at the edge of the slide but will flood off it unexpectedly, carrying 

 the sections with it onto the surface of the hot plate. 



Another procedure, which is not recommended for the inexperienced, is to 

 blot the sections before putting them on the hot plate. If one takes the slide 

 after the water has been drained from it and lays on its surface a water-saturated 

 piece of coarse filter paper, one can then press hard on the paper with a rubber 

 roller, squeezing much of the water out of both the paper and the sections. 

 This assures that the sections are perfectly flattened in contact with the slide, 

 but requires a strong nerve to try for the first time because of the fear that 

 the sections will stick to the paper. This has not happened in a good many 

 thousand slides which the author has made by this means, and slides so pre- 

 pared are always free of air bubbles. 



Before proceeding to a discussion of the next steps to be taken, it may be 

 well to review the innumerable things that may happen to prevent the pro- 

 duction of a perfect ribbon. The appearance, cause, and cure of the more 

 common defects are shown in Table 1. These are by no means the only defects 

 or the only cures which may be applied and every user of the microtome should 

 have in his hands O. W. Richards' "The Effective Use and Proper Care of the 

 Microtome," 1949, which lists many suggestions beyond those here given. 



Staining and Mounting Sections. Assuming that all the difficulties men- 

 tioned in the last section have been overcome and that one now has a series 

 of slides bearing dried consecutive ribbons, the next thing to be done is to 

 remove the paraflfin in order that they may be stained. It is conventional though 

 probably not necessary to warm each slide over a flame (holding it as shown 

 in Fig. 43) until the paraffin is melted thoroughly. Then the slide is dropped, 

 as shown in Fig. 51, into a jar containing xylene, benzene, or some other 

 suitable paraffin solvent. 



It is necessary through the subsequent proceedings to be able to recognize 

 instantly that side of the slide on which the section lies. This is not nearly as easy 

 as it sounds, and a lot of good slides have been lost by having the sections rubbed 

 off them. The simplest thing to do is to incline the slide at such an angle to 



