278 MICRO-CHEMICAL REAGENTS. 
chloric acid, and a freshly prepared solution of phloroglucin in 
100 parts of water dropped upon them, whereupon lignified 
membranes become red. Occasionally, this coloration appears 
without the addition of phloroglucin, for the reason that this 
principle itself occurs in some barks. 
CoLoRING AGENTS. 
35. Aniline Colors. Fuchsine, methyl-violet, methyl-green, 
Hanstein’s aniline-violet (equal parts of methyl-violet and 
fuchsine), vesuvine, as also aniline-blue and aniline-brown, re- 
ceive manifold applications, particularly in bacteriological inves- 
tigations, since these organisms are capable of strongly absorb- 
ing the aniline colors. But in histological investigations the 
above-named colors are also employed, usually dissolved in 100 
parts of water. 
_ 36. Eosin in aqueous solution colors dead protoplasm 
intensely red, and is therefore especially applicable, for example, 
in the examination of sieve-tubes. 
37. Carmine Solution. The best carmine is dissolved in 
ammonia-water, the clearly decanted liquid evaporated to 
‘dryness, and the residue (preferably only as required) dissolved 
in 100 parts of hot water. This reagent is abundantly absorbed 
by many substances, for example by albumen and resins, also 
by the delicate cuticle of cells, so that, by an unequal coloration 
of the walls and constituent substances, many relations may be 
rendered clearer. 
38. Hematoxylin (3.5 parts in 100 parts of water) in com- 
bination with alum is an admirable coloring agent for cell- 
nuclei. 
MountTinG MEDIA. 
If it is desired to keep a preparation, it must be preserved in 
a medium which does not evaporate, and in which the structure — 
_ of the preparation may be clearly retained. The most convenient 
to use for this purpose are certain preserving liquids, especially : 
_ glycerin (specific gravity 1.250) or calcium chloride (one part of 
