INTRODUCTORY. 7 



proceed to the higher grades of alcohol before staining, if 

 that can be avoided), and passed through a bath of stain, 

 then dehydrated with successive alcohols, passed through a 

 clearing medium into paraffin, cut, and treated as above 

 described, the sections in this case being mounted direct 

 from the chloroform, xylol, or other solvent with which the 

 paraffin is removed. If aqueous staining media be applied 

 (and this is sometimes desirable), the structures should either 

 be stained in toto immediately after fixing and washing out, or 

 sections may be stained on the slide, the objects, if delicate, 

 being passed through successive baths of alcohol of gradually 

 decreasing' strength before being put into the aqueous stain. 



In rny opinion it is generally advisable not to stain in 

 bulk material that is intended to be sectioned ; by staining 

 it as sections the staining can be much better controlled, and 

 many excellent stains can in this way be employed that are 

 not available for staining in bulk; and of course sections can 

 be stained much more rapidly than material in bulk. 



Balsam mounts of which the stain has faded, or which it 

 may be desired to submit to some other staining process, or 

 mount in some other medium, may often with great advan- 

 tage be re-strained and re-mounted. All that is necessary is 

 to put the slide into a tube of xylol or benzol till the cover 

 falls off (about two days), wash well for some hours in clean 

 xylol, and pass through alcohol into the new stain. Since 

 this was pointed out to me by Dr. Henneguy I have 

 unmounted and re-stained a large number of old prepara- 

 tions, and have succeeded in every case with series of 

 sections mounted on Mayer's albumen, or by the water 

 method. For shellac-mounted series, see E. MEYER, Biol. 

 Centralb.j x, 1890, p. 509, or last edition. 



The most convenient vessels, I find, in winch to perform the various 

 operations of staining, differentiating, dehydrating, clearing, etc., on the 

 slide, are flat-bottomed corked glass tubes. I have mine made 10 centi- 

 metres high and 27 millimetres internal diameter. Each of these will 

 then take two slides, English size, placed back to back. 



7. Resume of the General Method.- -To sum up, you may 

 either fix, wash out, stain, wash, dehydrate, clear, imbed, cut 

 sections, clear and mount them in balsam ; or fix, wash, 

 dehydrate, clear, imbed, cut, stain, wash, dehydrate, clear, 

 and mount according to choice. 



