PREPARATION AND STAINING OF TISSUE SECTIONS, 59 



are far more rapidly stained, and are easily over- 

 stained. In the latter case they must be treated 

 with a half-saturated solution of carbonate of 

 potash. In either case the sections are next washed 

 with distilled water, and passed through 60 per cent, 

 alcohol into absolute alcohol. When almost de- 

 colorised spread out the section carefully on a 

 copper lifter and transfer it to clove-oil, or stain 

 with picro-carmine solution (Weigert's) for half-an- 

 hour, wash in water, alcohol, and then treat with 

 clove-oil. After the final treatment with clove- oil, 

 transfer with the copper lifter to a clean glass slide. 

 Dry the preparation by pressure with a piece of 

 filter paper folded four times, and preserve in Canada 

 balsam dissolved in xylol. 



Gram's Method. In the method of Gram the 

 sections are stained for three minutes in aniline- 

 gentian-violet solution. This is prepared by shak- 

 ing up one ccm. of pure aniline with twenty four 

 parts of water, and filtering the emulsion. Half a 

 gramme of the best finely powdered gentian violet 

 is dissolved in the clear filtrate, and the solution 

 filtered before use. The sections are then trans- 

 ferred to a solution of iodine in iodide of potassium 

 till they become dark brown in colour, and then 

 decolorised in absolute alcohol. The time required 

 for complete decolorisation in alcohol varies from 

 a few minutes to twenty-four hours. They are 

 then treated with clove-oil and mounted in Canada 

 balsam. It is much better, however, to employ 



