133 



though the paraffin has apparently been dissolved at the end 

 of tnree or four minutes. (The slide can be left in xylol, if 

 the work must be interrupted, for several hours or even a 

 day without injury.) Turpentine or toluol can be used in- 

 stead of xylol. From the xylol remove the slide to a jar of 

 absolute alcohol (or 96^ alcohol may be used), which will re- 

 move the xylol. The slide should remain in the alcohol at 

 least five minutes. It may remain longer without harm. It 

 should then be transferred to a jar of 90^ alcohol for a few 

 minutes and then to a jar of 70^ alcohol for a few minutes. 

 The sections are now ready for staining. 



Staining. — The number of different " stains " described 

 in a manual of technic such as Lee's Vade-Mecum is so large, 

 and the recommendations regarding their use often so con- 

 fusing in the uniformity of commendation, that the begin- 

 ning student of histology is thoroughly at a loss when it 

 comes to making selection from such an embarras de richesses. 

 For general work in insect histology there is little demand 

 for that large and growing series of so-called strictly 

 chromatin stains, so essential in cytological work. A few 

 nuclear stains, in the wider sense of the phrase, a few 

 plasma stains, a stain which will certainly distinguish chitin, 

 and a stain or two especially for staining in toto, are all that 

 the beginner needs for most of his work. 



Having selected a stain, the student should bring the slide 

 from the 70^ alcohol (see above) into the jar of staining 

 fluid. Here the slide must remain until the sections are 

 thoroughly stained (for time required, see in account of. 

 each stain). Some workers pour a little of the staining fluid 

 on to the slide, but the use of small jars full of staining 

 fluid is much to be preferred. After the sections are 

 stained, they must be washed in 70^ alcohol or water, 

 depending upon the character of the staining solution (see 

 directions in case of each stain). They must then be 



