148 



THE ART OF MAKING MICROSCOPE SLIDES 



Mounting 



70 % alcohol each time a section is cut, and 

 each section must be individually removed 

 to a beaker of 70% alcohol in order to 

 avoid evaporation and drying. 



Staining Sections 



It is usually desirable to stain objects 

 before celloidin sections are cut, but when 

 it is necessary to stain subsequently, and 

 the sections have been prepared in 70% 

 alcohol as described, they may be sub- 

 mitted to the action of any staining fluids 

 exactly as though they were freehand sec- 

 tions. That is, they may be passed from 

 one solution to another with the aid of a 

 section hfter, washed in water, and in 

 general handled with considerable rough- 

 ness without any risk of damaging them. 

 It must be remembered, of course, that 

 alcohol solutions may not be employed 

 or the celloidin will be hopelessly softened. 

 The chief objection to this procedure is the 

 tendency of some stains to be absorbed 

 by the celloidin; it is cUfficult to find a 

 plasma stain which will stain tissues with- 

 out coloring celloidin. Nuclear staining is 

 relatively easy, as is also metal staining, 

 which is the process most usually applied 

 to celloidin sections. No attempt should 

 be made to flatten the section before it 

 has been stained, but it should be passed 

 through all the required techniques and 

 then returned to 70% alcohol before 

 mounting. A method of double staining a 

 botanical specimen is given in the typical 

 preparation which concludes this chapter. 



Mounting Celloidin Sections on Slides 



If the section has been cut in cedar oil 

 from an object which has been prestained, 

 nothing further is required than to remove 

 the section from cedar oil, place it in the 

 center of a clean slide, add a drop of the 

 resinous mounting medium selected, and 

 apply the coverslip. Anj^ sUght curl Avhich 

 tends to lift the coverslip may be easily 

 pressed out, either by leaving a weight on 

 the coverslip overnight or by using a small 

 spring clip to hold the covership down. 



If the section has been cut dry it will 

 usually be found too curled to mount satis- 

 factorily, and a different technique must 

 be followed. In this case the section is 



})laced in the approximate position on 

 the slide, and the slide, with the section, 

 placed in a small dish containing a little 

 ether. Within a relatively short time the 

 celloidin will have been softened suffi- 

 ciently to be pressed flat on the slide and 

 mounted in balsam under the coverslip. 



If the section has been cut in 70% alco- 

 hol, and subsequently subjected to various 

 staining procedures, it is necessary that 

 it should be dehydrated before being 

 mounted in balsam. It may be removed 

 from 70% alcohol to a mixture of equal 

 parts of absolute alcohol and chloroform, 

 the former to dehydrate the specimen, the 

 latter to prevent the dissolution of the cel- 

 loidin. This mixture will often appear 

 cloudy when the section is first put in, in 

 which case it is only necessary to replace it 

 with fresh solution and so on until both 

 the section and the specimen remain un- 

 clouded. When an unclouded condition 

 has been reached, the specimen may be 

 dehydrated in oil of cedar, placed on 

 the slide, and mounted as previously 

 described. 



It is occasionall}^ necessary, though usu- 

 ally undesirable, to attach a number of 

 celloidin sections to sHdes and then to 

 stain them in position. The reason this is 

 unsatisfactory is that it is hard enough to 

 remove staining dyes from the celloidin 

 matrix when both sides of the section are 

 free in a watchglass, and nearly impossible 

 when one side has been pressed against a 

 glass surface. This method, however, must 

 be employed if it is desired to serialize 

 celloidin sections and some cogent reason 

 prevents the use of the double technique 

 described in the next chapter. Of the vari- 

 ous methods given in Chapter 28 under 

 the heading V 21.2, the writer prefers that 

 of Heringa and ten Berge 1923 in which 

 clean slides are coated with a 3 % solution 

 of gelatin and dried. When these slides are 

 required they are soaked for a couple of 

 hours in 5% sodium sulfate, rinsed, and 

 again dried. The section is taken from 

 70% alcohol, pressed firmly to the sUde — 

 or the sections are lined up in their order 

 and pressed firmly to the slide — and then 

 dipped as soon as they are partially dry 

 once or twice in absolute alcohol and 

 chloroform. This gives a very reasonable 



