FORMULAE OF STAINS. 97 



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. 



Another method of dehydration is that introduced by 

 Unna. Here the section placed on the slide is dried in a 

 current of air, or by gentle heating over the flame. This 

 of course obviates all danger of decolorisation, but the 

 tissue elements are shrunken and distorted, and the method 

 therefore cannot be recommended. 



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. 



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

 binations. 



i . Loffler's Methylene-blue. 



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



Solution of potassium hydrate in distilled water (i -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.) 



Sections may be stained in this mixture for from a quarter of an 

 hour to several hours. They do not readily overstain. The tissue con- 

 taining the bacteria is then decolorised with^-i per cent acetic acid, 

 till it is a pale blue-green. The section is washed in water, rapidly 

 dehydrated with alcohol or aniline oil, cleared in xylol, and mounted. 



The tissue may be contrast-stained with eosin. If this is desired, 

 after decolorisation wash with water, place for a few seconds in I per 

 cent solution of eosin in absolute alcohol, rapidly complete dehydration 

 with pure absolute alcohol, and proceed as before. 



Films may be stained with Loffler's blue by five minutes' exposure or 

 longer in the cold. They do not usually require decolorisation, as 

 the tissue elements are not overstained. 



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