398 APPENDIX. 



stain in 100,000 of water. (3) The gelatinous sheaths of living 

 Spirogyra and other Algae can be stained with dilute methylene 

 blue without injuring the living protoplasm. 



Methyl Green, in strong alcoholic solution, is a good general 

 stain, especially useful for fresh material. (1) Alcohol-preserved 

 material should be treated with the stain for 15 or 20 minutes, then 

 washed with water and mounted in glycerine. (2) Fresh material 

 should be mounted in 2 per cent, acetic acid, to which a little of the 

 stain has been added. The nuclei are simultaneously fixed and 

 stained ; wash with 1 per cent, acetic acid and mount in glycerine. 

 The nuclei of Algae and Fungi are well brought out, being stained 

 green or blue-green, while the protoplasm is unstained. 



Methyl Violet. (1) In strong aqueous solution, this is good for 

 staining starch grains ; if the grains are then treated with dilute 

 calcium nitrate solution, the stain is deposited in the less dense 

 layers of the grains. For (2) sieve-tubes and (3) lignih'ed walls, 

 dissolve dry methyl violet in strong sulphuric acid the solution 

 will be brownish green, but on adding water the violet colour 

 appears ; treat sections with this and wash with water the cell- 

 walls are made swollen and transparent, the protoplasm is deeply 

 stained, sieve plates are brought out well, and lignified walls are 

 usually stained bright yellow. 



Milloii's Reagent. Dissolve 1 c.c. mercury in 9 c.c. strong 

 nitric acid, and add 10 c.c. water. This reagent may be bought 

 ready prepared, but it is better to make it up as required, since it 

 acts best when fresh. Proteins are stained brick-red the reaction 

 is hastened by heating. 



Nigrosin. See Picro-nigrosin. 



Nitric Acid, generally in 5 or 10 per cent, solution, has a variety 

 of uses. It (1) colours cutinised walls yellow ; (2) colours proteins 

 yellow see xanthoproteic reaction, 41, c ; (3) causes swelling of 

 cellulose and lignified walls ; (4) dissolves crystals of calcium 

 oxalate ; (5) is used with potassium chlorate in maceration, and as 

 a test for suberin. 



Olive Oil is used (1) for experiments on oils and their emulsifi- 

 cation and digestion see 85, 86 and (2) for mounting sections 

 of oily seeds containing protein grains. 



Orciu, dissolved in alcohol, is used as a test for inulin. Sections 

 are soaked in the solution and then warmed with strong hydro- 

 chloric acid ; an orange-red colour indicates presence of inulin. 



Osinic Acid, used generally in 1 or 2 per cent, solution in water, 

 serves for (1) fixing and hardening the protoplasm and nucleus; 

 (2) staining oils black. Osmic acid darkens various organic sub- 

 stances, and is therefore by itself an unreliable test for oils. It is 

 sold in sealed glass tubes containing one gram. To make up a 2 per 

 cent, solution, place 10 c.c. of water in a thoroughly clean bottle, 



