82 



PRACTICAL HISTOLOGY. 



to practise the slower method of staining sections in very dilute 



solutions of a dye. 



There is one method of staining sections which may be profitably 



impressed upon the student, viz., that so strongly insisted upon by 



Ranvier. Suppose any 

 delicate object isolated 

 epithelial or other cells 

 to be mounted in a 

 watery medium ; a drop 

 of a solution of picro- 

 carmine is placed at one 

 side of the cover-glass. 

 As the fluid evaporates 

 at one side of the cover- 

 glass the picro-carmine 

 slowly diffuses under the 

 cover-glass and stains 

 the preparation. Ex- 

 posed to the air, the 

 preparation would soon 

 become dry. This must 

 be corrected. This is 

 best done by placing 

 the slides to be stained 

 in this way on a stage 

 with several shelves 



(fig. 47), the whole being placed on a plate moistened with a few 



drops of water and covered by a bell-jar. This forms a moist 



chamber. 



After the cells are stained, glycerine may then be applied at the 



side of the cover-glass, with the same protective precautions, so 



that the preparation can be finally mounted and preserved in 



glycerine. 



FIG. 47. Support of Ranvier for Holding Slides Placed 

 under a Bell-Jar. 



XIII. CLEARING OR CLARIFYING REAGENTS. 



Glycerine, Farrant's Solution, and Glycerine Jelly. When 

 any one of these reagents is used for mounting preparations, no 

 other clarifying substance is used. 



Balsam Preparations. When a preparation is to be mounted 

 in balsam, be it Canada balsam or dammar, some clarifying reagent 

 has to be added to the preparation before the balsam is applied. 

 Before applying the balsam the tissues must have been rendered 

 transparent. 



