V] STAINING UN-IMBEDDED SECTIONS 39 



overstain the sections and then to decolourize them to the required 

 extent. Sections are left in a solution of saffranin 1 in 75 p.c. alcohol 

 or in an aqueous solution of methylene blue for 2 to 24 hours 2 . 

 They are then passed through the series of alcohols. In these the 

 colour is more or less rapidly extracted and the sections must be 

 passed through the fluids, the more quickly the more rapidly the 

 extraction is observed to take place. Clove oil dissolves these staining 

 agents, so that cedar wood oil or xylol, in which they are insoluble, 

 should be used as the clearing agent, in place of clove oil. Sections 

 of a young salamander may be stained ; the changes in the nucleus 

 during division will be seen. 



5. Staining sections and mounting them in 

 glycerine. Take two sections stained as in 1, remove 

 them from the staining agent to water, stir the water 

 with a glass rod till no more colouring matter comes 

 from the section (a minute or two); then (a) place one 

 in a watch-glass with a drop of glycerine, and move it 

 gently about till the glycerine has penetrated it ; place 

 a small drop of glycerine on a slide, to this remove 

 the section on a needle, spread out the section, and 

 cover with a cover-glass. Sections stained with any 

 carmine stain may advantageously be mounted in 

 formic glycerine (glycerine containing 1 p.c. of formic 

 acid 1'16 sp. gr.). 



6. Treat the other section similarly, but with 

 dilute glycerine (equal volumes of glycerine and water) 

 instead of with strong glycerine; use a lifter to transfer 

 the section to the slide ; remove excess of fluid and 

 cover. 



1 A saturated solution of saffranin in 75 p.c. alcohol, diluted with 

 an equal volume of 75 p.c. alcohol. 



2 A 1 p.c. solution diluted so that sections placed in it in a watch- 

 glass are visible. 



