Staining Blood and Epithelium, etc. 157 



small piece on a slide, tease it up, and examine with a low 

 power until you find a nerve fibre terminating in an end- 

 plate on a muscle-fibre, separate it from the surrounding 

 fibres as much as possible, add some Farrant's medium or 

 glycerine jelly, and apply a cover-glass. 



If cornea or cartilage, make vertical and horizontal 

 sections with a freezing microtome, and mount in Farrant's 

 medium or glycerine jelly. Sections of gold-stained tissues 

 may also be mounted in Canada balsam ; when this is 

 desired, dehydrate in strong spirit, clear in clove-oil, and 

 mount in Canada balsam. 



There are many ways of staining with gold, but the 

 above is the most simple, and it gives very good results. 

 For the other methods the student may refer to the larger 

 works on practical histology. 



Staining with Picrocarmine. Eub up 1 gramme of 

 carmine with 10 c.c. of water, and 3 c.c. of strong liquid 

 ammonia ; add this to 200 c.c. of a saturated solution of 

 picric acid in distilled water. Leave the mixture exposed 

 to the air until it evaporates to one-third of its bulk ; 

 filter, and keep in a stoppered bottle. Place some of the 

 picrocarmine in a watch-glass, and immerse the section for 

 from half an hour to an hour. Eemove from the stain with 

 a lifter, and place the section on a slide ; drain away as 

 much of the excess of stain as possible, and, if necessary, 

 soak up what remains with a piece of filter-paper. Then 

 add a few drops of Farrant's medium, and apply the cover- 

 glass. 



Picrocarmine stained tissues should never be washed ; 

 if they are, all the yellow colour will be removed, and the 

 specimen will come out stained with carmine only. They 

 improve by keeping, and the staining process goes on for 

 several days after they are mounted ; that is to say, some 

 parts give up the stain, and others absorb it. Picrocarmine 

 may be purchased in crystals, with which a 2 per cent, 

 solution in distilled water should be made. 



If it is desirable to mount a picrocarmine stained section 



