Stains and Staining 39 



questions for another chapter. The formulae are largely empirical. 

 Some of those given here are taken from The Microtomist's Vade- 

 Mecurn (Lee), which is easily the most complete compendium of 

 stains and other reagents concerned in microtechnic. It is to be 

 regretted that botanists have no book of this character, but it must 

 be confessed that we have not the material for such an extensive 

 work. Other formulae are from Botanical Microtechnique (Zimmer- 

 mann) and from Stirling's Histology, and still others are from our 

 own laboratory. The directions for using a stain apply to stains 

 made up according to the formulae which are given here, and may 

 need modification if other formulae are employed. It is hoped, how- 



^ 



ever, that the directions will give the student sufficient insight into 

 the rationale of staining to enable him to make any necessary modi- 

 fications. 



The current practice in staining paraffin sections on the slide 

 differs from the practice in staining freehand sections or small 

 objects which are to be mounted whole. In case of paraffin sections, 

 the cell contents are usually as important and often more important 

 than the cell walls; consequently, extreme care must be given to 

 every detail. With freehand sections the cell contents often drop 

 out, but even when they remain the cell walls are usually the impor- 

 tant features; and so the process is considerably shortened. 



For staining freehand sections, it is customary to use solid 

 watch glasses, unless the sections are very large. The details of 

 the method are given in chap, vi, on " Freehand Sections." 



For staining sections on the slide, nothing is better than the 

 ordinary Stender dish. The arrangement of Stender dishes shown 

 in Fig. 14 is very convenient. The advantage is obvious. With 

 two dishes each of xylol, xylol-alcohol, and absolute alcohol, one 

 set can be used in passing down to the stain, and the other, which 

 is thus kept free from any paraffin in solution, can be used in passing 

 back to the balsam. Even for paraffin sections, some use only 

 three alcohols, 50, 95, and 100 per cent, and the first two may be 

 simply poured over the slide; in this case, only one Stender dish- 

 for the 100 per cent alcohol is necessary in the alcohol series, the 

 other two alcohols being kept in bottles. This short method gained 



