REAGENTS AND PROCESSES 549 



to a second dish of water, and then mounted in a drop of water, as needed for exam- 

 ination. The cells may easily be separated from each other by teasing out the 

 section in the drop of water with two dissecting needles. The cells may be iso- 

 lated from each other by this treatment, for the reason that the middle lamellae 

 are dissolved, and only the membranes due to secondary thickening remain. The 

 lignin is also removed from the lignified membranes, so that these after maceration 

 give only a cellulose reaction. All chemical manipulations involving the evolution 

 of acid fumes as above should be carried on where the fumes may be quickly con- 

 ducted out of the laboratory, since the fumes are not only irritating to the mucous 

 membranes, but they are also injurious to delicate apparatus, such as compound 

 microscopes. 



Chromic acid may be used for maceration instead of Schulze's maceration fluid. 

 A concentrated aqueous solution is used, and in this the sections are allowed to re- 

 main for about half a minute, when they are to be rinsed in plenty of water. They 

 are then to be teased out in a drop of water as before. Very thick sections can not 

 be treated by this method. 



Schulze's maceration fluid is to be particularly recommended for sections con- 

 taining lignified tissues, while tissues destitute of lignified membranes, or containing 

 only a small percentage of these, may be better macerated as follows: A mixture is 

 made of i part of hydrochloric acid and about 4 parts of alcohol! The sections 

 remain in this mixture for about twenty -four hours ; then they are washed in water, 

 and mounted in a 10 per cent, solution of ammonia. A slight pressure on the cover- 

 glass will assist the cells in separating from each other. Cork-cells can be macer- 

 ated to best advantage by means of a dilute solution of potassium hydrate. See 

 also under Acetic Acid. 



Magdala Red. Make a saturated solution in 85 or 90 per cent, alcohol. Mix 

 I to 3 drops of this stain with about 20 mils of 90 per cent, alcohol and let the stain 

 act 3 to 6 hours or longer. Pour off the stain and put the material in a mixture of 

 Venetian turpentine, I part, and absolute alcohol, 9 parts, and allow the turpen- 

 tine to concentrate. If overstaining should occur, it may be corrected by placing 

 the preparation on a white background in the direct sunlight. Especially use- 

 ful in staining algae. 



Magnesium Sulphate and Ammonium Chloride. A mixture of 25 volumes 

 of a concentrated aqueous solution of magnesium sulphate, 2 volumes of a concen- 

 trated aqueous solution of ammonium chloride, and 15 volumes of water is used as 

 a test for phosphoric acid in tissues. When sections containing salts of phosphoric 

 acid are treated with this reagent, a crystalline precipitate of ammonium mag- 

 nesium phosphate is formed. 



Mercuric Chloride. Used as a fixative in both aqueous and alcoholic solutions. 

 An aqueous solution which has given excellent results is composed of 80 parts of a 

 saturated aqueous solution of mercuric chloride in water and 20 parts of glacial 

 acetic acid. See also under Fixatives. 



Methyl -alcohol. The refractive index of methyl-alcohol is 1.321, being less 

 than that of water, which is i .336. On account of this low refractive index methyl- 

 alcohol is a good mounting medium for bringing out the striation in starch-grains 

 and cell-walls. 



Methyl-blue. An excellent stain for cellulose membranes. For double stain- 

 ing, the sections may first be stained with safranin, then washed with alcohol and 

 placed in a concentrated aqueous solution of methyl-blue for 15 minutes or longer. 

 The sections are then to be washed in strong alcohol and mounted in Canada 

 balsam. See also under Double Staining. 



Methylene-blue. A good nuclear stain. For cells filled with protein granules 

 it is particularly good in differentiating the nucleus. Methylene-blue is useful in 



