4 INTRODUCTORY 



At this point the course of treatment follows one of two different 

 roads, according as the object is to be mounted direct in balsam or is 

 first to be sectioned (§ 5). 



5. Imbedding, and Treatment of Sections. The objects are 

 now imbedded. They are removed from the clearing medium 

 and soaked until thoroughly saturated in the imbedding medium. 

 This is, for small objects, generally paraffin, liquefied by heat, 

 and for large objects either paraffin or a solution of collodion or 

 " celloidin " (in this last case the clearing may be omitted and 

 the tissues be imbedded direct from the alcohol). The imbedding 

 medium containing the object is then made to solidify, and 

 sections are made with a microtome through the imbedding mass 

 and the included objects. The sections are then mounted on a 

 slide by one of the methods described in the chapter on Serial 

 Section Methods, the imbedding material is removed from them 

 (in the case of paraffin), they are stained in situ on the slide, 

 dehydrated with alcohol, cleared, and mounted in balsam or 

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

 in watch-glasses, and afterwards mounted as desired— the imbed- 

 ding medium being first removed if desirable. 



Or, the material may be stained in bulk, before cutting the 

 sections. 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, 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. 



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 medimn, may often with great advantage be re-stained 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 



