CHEMICAL RE- AGENTS. 245 



glycerine, or in gelatine and glycerine. The most im- 

 portant points in any such injections are shown if the 

 preparation be dried and mounted in Canada balsam. The 

 specimen must, in the first place, be well washed and 

 floated upon a glass slide \vith a considerable quantity of 

 water, which must be allowed to flow off the slide very 

 gradually. The specimen may then be allowed to dry 

 under a glass shade, in order that it may be protected 

 from dust. The drying should be effected at the ordinary 

 temperature of the air, but it is much expedited if a 

 shallow basin filled with sulphuric acid be placed with it 

 under a bell-jar." 



Chemical Re-agents. The following chemical re-agents 

 and preservative fluids are recommended for microscopic 

 uses i 1 



1. Alcohol, principally for the removal of air from 

 sections of wood and other preparations ; also as a solvent 

 for certain colouring matters. 



2. JEther, chiefly as a solvent for resins, fatty and other 

 essential oils, &c. ; also useful for the removal of air. 



3. Solution of Caustic Potass, as a solvent for fatty 

 matters; also of use occasionally in consequence of its 

 action upon the rest of the cell-contents and thickening 

 layers. This solution acts best upon being heated. 



4. Solution of Iodine (iodine one grain, iodide of potas- 

 sium three grains, distilled, water one ounce) for the 

 coloration of the cell-membrane and of the cell-contents. 



5. Concentrated Sulphuric Acid, employed chiefly in the 

 examination of pollen and spores. 



6. Diluted Sulphuric Acid (three parts acid, one part 

 water), for the coloration of cells previously immersed in 

 the iodine solution. The preparation is first moistened 

 with the iodine solution, which is afterwards removed with 

 a hair pencil, and a drop of sulphuric acid added by means 

 of a glass rod ; the preparation is then immediately covered 

 with a piece of glass. The action of the sulphuric acid 

 and iodine, as well as that of the iodised chloride of zinc 

 solution, is not always uniform throughout the whole 



(1) A set of 12 test-bottles, packed in a small box, is supplied by Mr. 

 Matthews of Portugal Street, Lincoln's Inn Fields, the price of which is only a 

 few shillings. 



