108 A MANUAL OF BACTERIOLOGY 



Treatment of Sections for Staining and 

 Mounting 



(a) Frozen sections. If preserved in spirit they should 

 be rinsed in distilled water or in fresh alcohol before 

 staining, according as the staining solution is an aqueous 

 or an alcoholic one. After staining they are well rinsed 

 in water or alcohol to remove the excess of stain, and are 

 then dehydrated and cleared before being mounted. For 

 dehydrating, if they have been washed in water, they 

 should be well rinsed in methylated spirit l to remove the 

 excess of water, and then transferred to absolute alcohol 

 for a few seconds to two minutes, the time varying with 

 the size and thickness of the section. In many cases for 

 instance, when the anilin dyes have been used for staining 

 the sections must be passed as rapidly as possible, con- 

 sistent with thorough dehydration, through the absolute 

 alcohol to avoid removing too much of the colour. If 

 it is important to avoid any decolorisation, anilin oil may 

 be used for dehydration, as in Weigert's method (pp. 105 

 and 106). For clearing, xylol or cedar oil is the best agent, 

 for neither dissolves the anilin dyes ; they will only clear, 

 however, out of absolute alcohol : hence the preliminary 

 rinsing of water- washed sections with methylated spirit 

 to prevent dilution of the subsequent bath of absolute 

 alcohol. Oil of cloves can also be employed, but has the 

 disadvantage that it dissolves the anilin dyes, and the 

 colour of stained sections treated with it is apt to be less 

 permanent ; it has the advantage, however, of clearing 

 out of methylated spirit, absolute alcohol being unnecessary. 

 The alcohol and clearing agents are conveniently placed 

 in watch-glasses or small shallow glass capsules. The 



1 Absolute alcohol may of course be employed instead of the first 

 bath of methylated (or rectified) spirit, but methylated answers just 

 as well and is less expensive (but see note, p. 86). 



