APPENDIX. — MICRO-REAGENTS. 209 



Alter repeated agitation, it is set aside for twenty-four hours ; the clear liquid 

 is then decanted and mixed with two volumes of distilled water. It should be 

 kept in a close-fitting, glass stoppered bottle, the stopper of which has been 

 dipped in vaseline to prevent it from sticking. It may be used in the same 

 manner as the aqueous solution, by diluting it to suit the special requirements 

 of the case. It has the advantage of keeping better than the ordinary watery 

 solutions. 



Phloroglucin. Make a two or three per cent, solution in alcohol. It is 

 the best available test for lignified tissues. The section to be tested is first 

 treated with a few drops of the solution, and after the tissues have been 

 thoroughly permeated by it, a drop of hydrochloric acid is applied. All lignified 

 tissues will immediately be stained a beautiful red color, which will vary in 

 depth according to the degree of lignification, while unlignified tissues are not 

 stained at all. The middle lamella of thickened cell-walls is often beautifully 

 differentiated from the rest of the wall because of its deeper staining. 



An alcoholic solution of aniline chloride used in the same manner stains 

 lignified tissues a bright yellow, while other tissues are unaffected. 



Schulze's Maceration Fluid. This consists of strong nitric acid in which 

 potassium chlorate has been dissolved to saturation. It acts powerfully on 

 vegetable tissues, but dissolves the middle lamella more readily than the rest 

 of the cell-wall, and hence is highly serviceable in isolating cells. The fluid acts 

 more rapidly if heat is applied, but better results are obtained if the process is 

 not hastened. It is often of advantage to dilute the solution somewhat with 

 water and let the tissues macerate for some hours. When the action has been 

 continued long enough, the tissues become colorless, and when placed upon a 

 slide and covered with a cover-glass, if the latter be gently tapped with a 

 needle-point the cells will readily separate. 



This reagent is also useful for the detection of suberized tissue. On boil- 

 ing a thin section in it, the corky tissues will be found to resist the action of 

 the reagent longer than the rest, but finally the cells swell up and their walls 

 liquify, forming an oily looking liquid called eerie acid. The test applied in 

 this way serves well for demonstrating strongly suberized tissues, but is not suf- 

 ficiently delicate for slightly suberized ones. These may be identified as 

 follows : Soak the section for a few moments in the cold fluid and then remove 

 it to solution of potassium hydrate ; the suberized tissues will immediately 

 assume an ochre-yellow color. 



Nitric Acid. This reagent is generally used in the concentrated form. 

 It immediately kills protoplasm, and causes it to shrink away from the cell-wall, 

 and if ammonia or potassium hydrate be afterward applied, the proteid cell 

 contents assume a yellow color. 



If a section containing thick-walled tissues be treated with hot nitric acid 

 and afterward with ammonia, the middle lamella will be stained yellow. 



Sulphuric Acid. Strong sulphuric acid dissolves starch and cellulose, 

 converting the former into dextrin and the latter into amyloid, a substance 

 which, like starch, acquires a blue color with iodine. It dissolves protoplasm 

 and other albuminoids much more slowly, hence it is is used for demonstrating 

 the continuity of protoplasm from cell to cell in certain tissues. It also stains 



