284 Modern Microscopy 



This is the best all-round clearing agent known; it 

 clears from 90 per cent, alcohol in one minute ; it does not 

 shrink tissues, nor does it affect stains. 



Drain off the clearing agent, place a little ridge of xylol- 

 balsam upon the middle of the slide from one end of the 

 sections to the other, gently lower the cover-glass, arrange 

 it into position with needles, and place the mount upon the 

 glass shelf above the oven, or even upon the top of the 

 oven, to evaporate the xylol ; subsequently finish. 



XYLOL-BALSAM FORMULA. 



Fill a 6-ounce corked bottle with dried balsam. 

 Add sufficient pure xylol to barely cover the balsam. 



It will be ready for use in a week or so. Balsam that 

 has been properly dried, free from oil in a sand-bath, must 

 be used ; the ordinary Canada balsam of commerce will 

 never dry if used. 



The rationale of the above double-staining process is as 

 follows : The nuclei are far more greedy for the stain than 

 the other elements of the organ ; consequently the nuclei 

 are stained first with a stain that does not affect the cyto- 

 plasm too deeply, and which does not readily wash out in 

 either water or alcohol during the subsequent operations. 

 Haematoxylin fulfils this requirement in a high degree. 

 Then it is necessary to counter-stain the remaining 

 elements with a stain having the following characteristics : 

 First, it must give good contrast in colour to the hsema- 

 toxylin ; second, it should have no tendency to wash out 

 or deteriorate the first stain ; third, it must stain quickly, 

 and not be liable to wash out in the dehydrating alcohols. 

 Bismark brown fulfils our second requirement. 



Of course glycerine- jelly and other mounting media may 

 be used instead of balsam. Such will necessitate a slightly 

 different method of procedure after the alcohol baths 

 No. 15. 



