556 POWDERED DRUGS 



solution of orseillin BB and a drop or two of aniline blue. The solution should have 

 a violet color. The sections may be mounted for examination in glycerine. 



Osmic Acid. The vapor of osmic acid may be used as a fixative for very 

 small organisms. In order to accomplish this a drop of water containing the 

 organisms need only to be inverted over a bottle containing a 2 per cent, solution 

 of the acid. Osmic acid colors ethereal and fatty oils from brown to black, but 

 other organic substances are also darkened by it ; and as a test for oils it is not 

 absolutely reliable. Aleurone grains in sections of Ricinus which have been 

 freed from their oil by standing for a time in strong alcohol may be stained brown, 

 and the crystalloid and ground substance differentiated by immersing the sections 

 for a short time in a i per cent, solution of osmic acid. 



Paraffin. Paraffin of about 52 melting-point sections to good advantage at a 

 temperature between 21 and 24C., or 70 and 75P. Good cells for hanging-drop 

 cultures may be made by placing glass slides on the turntable and spinning rings on 

 them by means of a camel's-hair brush dipped in melted paraffin. 



Pepsin. One part of pepsin -glycerine and 3 parts of water acidulated with 

 0.2 per cent, of chemically pure hydrochloric acid. When sections containing 

 protoplasts are subjected to this reagent at blood temperature, certain structures 

 of the protoplast which are insoluble in the reagent may be isolated from those which 

 are soluble. In the dividing nucleus the kinoplasmic spindle-fibers persist after 

 the chromosomes and nuclear plate have been dissolved by this reagent. By the 

 action of digestive ferments on aleurone grains the ground substance is first dis- 

 solved and then the crystalloid more slowly, while the limiting membrane of the 

 vacuole occupied by the aleurone grain persists. Digestive ferments are thus 

 found to be excellent reagents for demonstrating the difference in constitution of 

 the finer structures of the protoplast and protoplasmic cell-contents. 



Phloroglucin. This furnishes one of the most reliable tests for lignin. Sections 

 are placed in alcohol containing a trace of phloroglucin, transferred to a drop of 

 water on a slide, and covered with a cover-glass. A drop of hydrochloric acid is 

 then applied to the edge of the cover-glass, and, and the acid comes in contact with 

 the lignified membranes, these are colored with a bright violet red. 



Phospho-molybdic Acid. This is used as a test for proteids. Sections are 

 treated for an hour or two with a solution of i Gm. of sodium-molybdium phosphate 

 in 90 Gm. of distilled water and 5 Gm. of concentrated nitric acid. Proteid ma- 

 terials then take on the appearance of yellow granules. 



Picric Acid. The structures of aleurone grains are well differentiated by fixing 

 in a concentrated alcoholic solution of picric acid and subsequent staining with eosin. 

 The sections are to remain in the alcoholic fixative for several hours. They are 

 then to be washed out in alcohol and stained for a few minutes in a solution of eosin 

 in absolute alcohol. Then the sections are successively washed in absolute alcohol, 

 t transferred to oil of cloves, and mounted in Canada balsam. The ground substance 

 is dark red, the crystalloid yellow, while the globoid remains colorless. The 

 pyrenoids and chromatophores of algae may be simultaneously fixed and stained 

 by placing the algae for an hour or longer in a concentrated solution of picric acid 

 in 50 per cent, alcohol, to which has been added about 5 drops of a solution of 20 

 Gm. of acid fuchsin in 100 mils of aniline water. The aniline water is prepared 

 by shaking up 3.5 Gm. of aniline in 96.5 Gm. of water. The algae are then washed 

 in alcohol, transferred to xylol, then to a thin solution of balsam in xylol, and are 

 finally mounted in the thicker solution of Canada balsam in xylol. 



Alcohol is a better solvent of picric acid than water, and accordingly it gives 

 quicker results in washing out the acid from the fixed material than water does, but 



