APPENDIX MICRO-REAGENTS. 211 



Alcohol is also indispensable as a means of anhydrating tissues, preparatory 

 to mounting them in Canada balsam or other oleo-resinous mounting fluids. 

 For this purpose strong alcohol, at least 98 per cent., is required. 



The presence of inulin in tissues may also be demonstrated by its use. 

 Tissues contai ning it are soaked in strong alcohol for seven or eight days, which 

 causes the inulin to be precipitated in the cells in the form of sphere crystals. 



Sulphuric Ether. This is useful chiefly as a solvent for fats in the study of 

 organs like seeds, which often contain these matters in abundance. 



Glycerin. This is serviceable for clearing sections, as a preservative 

 medium, and as a medium for the permanent mounting of tissues, though for 

 the latter purpose glycerine jelly is in almost all cases to be preferred. It ren- 

 ders cell contents more transparent, and hence facilitates the study of cell walls. 

 A mixture of equal parts of glycerine and alcohol is useful for macerating hard 

 tissues that have been preserved in alcohol preparatory to sectioning. They 

 should be transferred to the mixture from twelve to twenty-four hours previous to 

 sectioning. 



Ferric Chloride Solution. This consists of a rather dilute aqueous solu- 

 tion to which a drop of nitric acid has been added. It is one of the best tests 

 for the presence of tannin in cells. If a drop be applied to a section con- 

 taining it a blue-black or a greenish- black precipitate will be produced in 

 the cells. 



Fehling's Solution. This is prepared as follows : Dissolve 34.64 grams 

 of pure copper sulphate and 200 grams of Rochelle salt in the smallest possible 

 quantity of distilled water. Also dissolve in 600 cu. cm. of distilled water a 

 sufficient quantity of sodic hydrate to make a liquid having the specific gravity 

 of 1. 12. Keep the solutions separately in well stopped bottles until required 

 for use. When required as a test for sugar, mix one part of the former with 

 two of the later liquid. This constitutes one of the best and most convenient 

 tests for detecting sugars in tissues, and for distinguishing between the saccharose 

 and the glucose groups of sugars. To apply the test dip a moderately thick 

 section of the tissue in the boiling hot solution for two or three seconds. If 

 grape-sugar be present the cell-contents will have been colored red from the 

 precipitation of the sub-oxide of copper, but if cane and not grape-sugar is 

 present a bluish or greenish color will be produced in the cells, but at first no 

 red precipitate. On soaking the section, however, in the hot solution for a 

 longer time a red precipitate gradually appears, because a part of the cane- 

 sugar is converted into invert sugar. 



Labarraque's Solution (Sodium Hypochlorite). It is prepared as fol- 

 lows : Intimately mix four parts of good chlorinated lime with fifty parts of 

 water, and in fifty parts more of boiling water dissolve five parts of sodium 

 carbonate. Mix the two liquids while the latter is still hot, and cover the vessel 

 tightly. After the solution has cooled add twenty-five parts more of water and 

 then allow it to stand until all sediment has settled. Draw off the clear solu- 

 tion and preserve in well stopped bottles protected from the light. The solution 

 is very useful in destroying cell-contents and in bleaching tissues. If sections 

 which have been bleached by it are afterwards to be stained they must first be 

 very thoroughly washed to remove all traces of the bleaching agent. 



