226 THE MICROSCOPE. 



over the lamp. When a few drops of pure glycerine have 

 been allowed to flow over it, the thin glass cover must be 

 re-applied and pressed tightly down. If the preparation 

 looks clear under an eighth o]l twelfth, the glass cover may 

 be cemented on, and the specimen left to dry. The success 

 of Dr. Eealft's process, it appears, much depends upon the 

 care and patience with which each stage of the soaking, 

 washing, warming, and pressure is carried out. Each point 

 of structural difference is gradually brought out by sub- 

 jecting the specimen to a little firmer pressure, or by 

 soaking it in a little fresh glycerine in a watch-glass, and 

 then applying gentle heat. By the aid of needles, and 

 a little careful manipulation, tissues may be laid out per- 

 fectly smooth and flat. 



A word about making and preparing Transparent In- 

 jections. — The great desideratum of a transparent injecting 

 fluid is, that it shall not, by the action of osmosis, dye the 

 tissue meant to be injected. This at once bars the use of 

 soluble colours, and necessitates the use of insoluble colour- 

 ing matter in an exceedingly fine state of subdivision. 

 The following composition is stated to succeed admirably, 

 showing vessels of WDijth of an inch diameter, with a 

 clear outhne even under a ^th objective, without a grain 

 of extravasation of the colouring matter: — Take 180 grains 

 best carmine ; J fluid ounce of ammonia, common strength, 

 sp. gr. 0*92 ; 3 to 4 ounces distilled water. Put these 

 ingredients into a small flask, and allow them to digest 

 without heat for 24 or 36 hours, or until the carmine 

 \s dissolved. Then take a Winchester quart-bottle, and 

 mark upon it the line to which 16 ounces of water 

 extend. The coloured solution must then be filtered 

 into the bottle, and pure water must be added until 

 the whole is equal to 16 ounces. Next dissolve 600 

 grains of potash-alum in about 10 fluid ounces of water, 

 and add to this, under constant boiling, a solution of 

 carbonate of soda, until a slight permanent precipitate 

 is produced. Filter and add water up to 16 fluid ounces. 

 ]joil, and add this solution, while boiling, to the cold 

 ammoniacal solution of carmine in the Winchester quart, 

 and shake vigorously for a few minutes. A drop now 

 placed upon white filter-paper should show no coloured 



