90 THE MICROSCOPE. 



then retain the quill, and withdraw the needle from the tube. I then 

 seize with 1;he small forceps the quill, and introduce into it the small 

 extremity of the syringe ; and push the piston with a force always 

 decreasing." 



By carefully following out these directions, any one, after a little 

 practice, will be enabled to succeed in making many useful and valuable 

 preparations. Injections are best viewed by the aid of the Leiberkuhn, 

 or under a condensed light with a one or two inch object-glass. For 

 Harting's process of injecting, see translations in the Edinhwgh Monthly 

 Journal, 1852. 



CHEMICAL KE- AGENTS. 



Dr. Schacht recommends the following chemical re-agents and pre- 

 servative fluids for microscopic uses : 



1. Alcohol, principally for the removal of air from sections of wood 

 and other preparations j also as a solvent for certain colouring matters. 



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

 oils, (fee. ; 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-con- 

 tents and thickening layers. This solution acts best upon being heated. 



4. Solution of Iodine (iodine one grain, iodide of potassium three 

 grains, distilled water one ounce) for the coloration of the cell-mem- 

 brane and of the cell-contents. 



5. Concentrated Sulphuric Acid, employed chiefly in the examina- 

 tion of pollen and spores. 



6. Diluted Sulphuric Add (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 after- 

 wards 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 uni- 

 form throughout the whole surface of the preparation. The colour is 

 more intense where the mixture is more concentrated ; it frequently 

 happens that many spots remain uncoloured. The colour changes after 

 some time, the blue being frequently changed into red after twenty- 

 four hours. 



7. A Solution of Chloride of Zinc, Iodine, and Iodide of Potassium. 

 A drop of this compound solution, added to a preparation placed in a 

 little water, produces the same colour as iodine and sulphuric acid. 



