GLYCERIN. 243 



animal pigments. If it really performs this, its great value is 

 evident. 



402. BRUN'S Glucose Medium (from FABRE-DOMERGUE'S Pre- 

 miers Principes du Microscope et de la Technique microscopique, 

 Paris, 1889, p. 123). 



Distilled water .... 140 parts. 

 Camphorated spirit . . . 10 



Glucose . 40 



Glycerin 10 ,, 



Mix the water, glucose, and glycerin, then add the spirit, 

 and filter to remove the excess of camphor which is pre- 

 cipitated on mixing. I am indebted to Dr. HENNEGUY for 

 calling my attention to this liquid, which is an important one. 

 It is preferable to glycerin because it preserves the colour of 

 preparations stained with anilin dyes, methyl green included. 



402 a. Levulose as a Mounting Medium. Levulose is recommended 

 as a mounting medium by BEHBENS, KOSSEL, u. SCHIEFFEBDECKEB (Das 

 MikrosJcop. u. d. Meth. d. miJc. Unters., Braunschweig, 1889). It is un- 

 crystallisable, and preserves well carmine and coal-tar stains (haeinatoxylin 

 stains fade somewhat in it). The index of refraction is somewhat higher 

 than that of glycerin. Objects may be brought into it out of water. 



Glycerin Media. 



403. Glycerin. Glycerin diluted with water is frequently 

 employed as an examination and mounting medium. Dilution 

 with water is sometimes advisable from an optical point of 

 view, on account of the increased visibility that it gives to 

 many structures by lowering the index of refraction of the 

 glycerin. But from the point of view of efficacious preserva- 

 tion it is always advisable to use undiluted glycerin, the 

 strongest that can be procured. 



Long soaking of tissues in glycerin of gradually increased 

 strength is a necessary preliminary to mounting in all cases 

 in which it is desired to obtain the best possible preparations, 

 and to ensure that they shall keep well. If this soaking is 

 done on the slide (the cover being removed and the object 

 treated with fresh glycerin every one or two days) , it is well 

 to take the precaution recommended by Beale, of luting the 

 edges of the cover so as to make the preparation air-tight, as 

 glycerin is so highly hygroscopic that a drop of it exposed to 

 the air rapidly diminishes in strength to a very considerable 



