io8 MICROSCOPIC METHODS. 



the slide moved to and fro. The section is dehydrated 

 and becomes clear. The process may be accelerated 

 by heating gently. The preparation is then treated with 

 a mixture of two parts of aniline oil and one part of xylol, 

 and then with xylol alone, after which it is mounted in 

 xylol balsam. 



Sections stained for bacteria should always be cleared, at 

 least finally, in xylol, for the same reason that xylol balsam 

 is to be used for mounting films, viz. that it dissolves out 

 aniline dyes less readily than such clearing reagents as 

 clove oil, etc. Xylol, however, requires the previous de- 

 hydration to have been more complete than clove oil, which 

 will clear a section readily when the dehydration has been 

 only partially effected by, say, methylated spirit. If a little 

 decolorisation of a section is still required before mounting, 

 clove oil may be used to commence the clearing, the process 

 being finished with xylol. 



We sometimes have to deal with bacteria which show a 

 special tendency to be decolorised. This tendency can be 

 obviated by adding a little of the stain to the alcohol, or 

 aniline oil, employed in dehydration. In the latter case a 

 little of the stain is rubbed down in the oil. The mixture 

 is allowed to stand. After a little time a clear layer forms 

 on the top with stain in solution, and this can be drawn off 

 with a pipette. 



When methylene-blue, methyl-violet, or gentian-violet 

 are the stains being used they can, after the proper 

 degree of decolorisation has been reached, be fixed in the 

 tissues by treating for a minute with ammonium molybdate 

 (2^ per cent in water). 



The Formulae of some of the more commonly used Stain Com- 

 binations. 



i. LoffleSs Methylene-bhie. 



Saturated solution of methylene-blue in alcohol . 30 c.c. 



Solution of potassium hydrate in distilled water (1-10,000) 100 c.c. 



(This dilute solution may be conveniently made by adding I c.c. of 

 a i per cent solution to 99 c.c. of water.) 



