188 The Microscope. 



mended the following as giving the most satisfactory results. 

 The finger is pricked and a large drop of blood is allowed to 

 exude ; a perfectly clean cover-glass is lightly drawn upon the 

 top of the drop so that a very thin layer of blood adheres, so 

 thin as hardly to be evident until it is dry. It is then dried in 

 the air or put at once without drying into one of the following 

 solutions, viz. chromic acid 1-12 per cent. ; bichromate of potas- 

 sium 1-2 per cent. ; methylated spirits or absolute alcohol for 

 five or ten minutes, washed in water and again dried. The 

 specimen is now ready for staining. The best dye for this pur- 

 pose will be found a recently prepared 1 per cent, solution of 

 Spiller's purple in water to which a few drops of alcohol have 

 been added, or a weak spirit solution of rosein. A few drops 

 of one or other dye having been filtered into a watch-glass, the 

 cover glass is placed upon the surface of the solution blood 

 downwards, and allowed to remain so for from five to ten min- 

 utes. It is then removed, washed for some time in a gentle 

 stream of distilled water, dried thoroughly, and mounted in 

 Canada balsam with or without previous treatment in clove oil 

 for a minute or two. On examination of the specimen the col- 

 ored corpuscles should be found of normal shape and colored 

 purple or red, according to the dye used, and the colorless cor- 

 puscles similarly stained. The method with Spiller's purple 

 will be found especially useful when blood is examined in dis- 

 eased conditions in which the existence of micro-organisms is 

 suspected, and is superior to any other of the many anilin dyes 

 (such as methyl- violet) which I have tried. 



REPAIRING A NICHOL PRISM. 

 Nichol prisms which have become scratched and dull may 

 be restored to usefulness by cementing a thin cover-glass over 

 the ends with clarified gum-damar. The prisms should first be 

 carefully cleaned by scrubbing with a very soft brush and soap, 

 to which may be added a little precipitated chalk. They should 

 then be rinsed with distilled water and carefully dried, pains 

 being taken to remove every particle of dust and dirt from with- 

 in the scratches. The cover-glass, which should be thin and per- 

 fectly clean, should then be applied in the usual way, exactly 



