4 INTRODUCTORY. 



damar. Or they may be stained, washed, dehydrated, and 

 cleared in watch-glasses, and afterwards mounted as desired 

 the imbedding medium being first removed if desirable. 



It is not always desirable to remove the imbedding mass ; celloidin sec- 

 tions stain well without being freed from it, and are usually even dehydrated, 

 cleared, and mounted without removal of the mass, which becomes quite 

 transparent in balsam. This plan has the advantage, which is a very impor- 

 tant one for large sections, of allowing the sections to remain during the 

 whole of the manipulations protected by a supporting mass that holds all 

 their pails together. 



The plan of staining sections on the slide is of somewhat recent introduc- 

 tion ; before it had been worked out the practice was to stain structures 

 in toto, before cutting sections. And in cases in which structures are suffi- 

 ciently small and permeable to allow of satisfactory staining in this way, and 

 if it be not essential to save time, this plan is sometimes as good as the one 

 described. In this case the object, after having been fixed and washed out, 

 is taken from the water, or while still on its way through the lower alcohols 

 (it should not be allowed to proceed to the higher grades of alcohol before 

 staining, if that can be avoided), and passed through a bath of stain (gene- 

 rally alcoholic borax-carmine or other alcoholic stain) of sufficient duration, 

 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 turpentine, naphtha, or other solvent with 

 which the paraffin is removed. If aqueous staining media be employed (and 

 it is sometimes very desirable for particular purposes to prepare specimens 

 with some aqueous stain) the structures should either be stained in toto 

 immediately after fixing and washing out, or sections may be stained on the 

 slide, the objects being passed through successive baths of alcohol of gradu- 

 ally decreasing strength before being put into the aqueous stain (a precaution 

 which will not be necessary for chromic objects (see below, 5) ). 



It was stated in the first edition of this work that " the great 

 majority of preparations are made by fixing either with subli- 

 mate or a picric acid combination, washing out with alcohol, 

 staining with alcoholic borax-carmine, imbedding in chloro- 

 form-paraffin, cutting with a sliding microtome, and mounting 

 the sections in series in Canada balsam." That is probably 

 still the case, but the method can no longer claim, to be what 

 it then appeared to be, the classical method of microscopic 

 anatomy. I suggest the following, as being quite as easy to 

 carry out, and as giving preparations far richer in detail and 

 more truthfully preserved : Fix in Flemming's chromo-aceto- 

 osmic mixture ; wash out with water ; dehydrate ; clear with 

 oil of cedar-wood ; imbed in paraffin ; mount sections on the 

 slide with Mayer's albumen medium ; stain with safranin, or 



