244 PRACTICAL HISTOLOGY [XXXI 



solution of aniline blue-black may also be used ; to avoid over- 

 staining a section should be examined now and then. 



Thin pieces may be stained in bulk with Bourne's picrocarrnine 

 or with borax carmine (p. 308), for one or more weeks, but the 

 result is not very satisfactory. 



Staining basophil cell-substance. Sections of the brain or 

 spinal cord may be treated in the way already described for 

 sections of spinal ganglia (Lesson xv. 3). 



As hardening agents are used : 



(a) Alcohol about 95 p.c. ; this however causes considerable 

 shrinking. If the cord is cut into thin pieces about half-an- 

 hour after being placed whole in the alcohol, the pieces will be 

 hardened in about a day. 



(>) A saturated solution of mercuric chloride in salt solution ; 

 it is best to place small pieces in this for a day, then transfer to 

 alcohol (cp. p. 297). 



(c) Formol 10 p.c. for 2 to 4 days, then alcohol 2 to 4 days. 



The piece of tissue may be imbedded in celloidin or paraffin. 

 Or it may be cut without imbedding, thus : one surface is partially 

 dried with blotting-paper, fixed to a piece of cork with fish-glue 

 or 'gum, left for half an hour in alcohol, then cut moistened with 

 95 p.c. alcohol. 



Instead of methylene blue, a saturated aqueous solution 

 of thionin or toluidin blue may be used, the sections are 

 differentiated in aniline oil and alcohol (p. 117), passed quickly 

 through absolute alcohol to xylol and balsfem. Or they may 

 be stained with a saturated aqueous solution of acid magenta, 

 differentiated for 1 to 2 minutes in absolute alcohol, passed 

 through clove oil to balsam. 



Sections stained with methylene blue, and differentiated with 

 aniline oil and alcohol, may be again stained and again differen- 

 tiated, then blotted, cleared quickly with cajeput oil, blotted, 

 cleared with benzin, and mounted in benzin solution of 

 colophonium. 



