396 MICROSCOPICAL TECHNIQUE. 



acidulated water is next added. The mixture is then boiled in a 

 Koch's steamer until the agar is dissolved, after which it is filtered 

 through a hot-water funnel, and 4 or 5 per cent, of glycerin added 

 to the filtrate. The medium is now ready for sterilising in test- 

 tubes in the ordinary way. Sometimes the serous fluid is very rich 

 in albumin. Before adding the potash, a little should, therefore, 

 be boiled in a test-tube ; if it becomes practically solid or contains 

 a large excess of albumin, it should be diluted with at least twice 

 its bulk of distilled water. — Pharmaceutical Journal. 



The Staining of Cellulose.— Varying results may be obtained 

 on staining cellulose, according to its age, young and soft tissue 

 absorbing stains with least difificulty, whilst maturer tissues may 

 remain unaffected by the same stains. Dr. E. G. Love studied 

 the subject, and made comparative tests with a view to determining 

 the value of different stains. He found that some stains — such as 

 hsematoxylin — require no mordant to fix them, whereas carmine 

 stains generally require a mordant, such as alum. The mordant 

 may be mixed and applied with the stain, or it may be used sub- 

 sequently; or, again, the tissue may be impregnated with the 

 mordant before the stain is applied. There are thus four ways of 

 staining tissues. The last-mentioned was found best for prepara- 

 tions which are difficult to stain. In the specimens of cotton and 

 linen fibres treated, the cellulose was, of course, not in such a 

 receptive condition as young and soft cellulose tissue, for in pro- 

 portion as the cellulose increases in density it affords a greater 

 resistance to the action of stains. Thus, Grenacher's solution of 

 carmine in alum was found to produce a slight reddish tint only 

 after twelve hours ; Thiersch's solution in oxalic acid a dull rose 

 colour after eighteen hours ; and borax carmine, with oxalic acid 

 as a mordant, was no better than Grenacher's solution. The 

 cotton fibres were stained light blue by hsematoxylin and alum, but 

 any depth of colour could be obtained by applying a mordant 

 (alum, aluminium, copper sulphate, or acetate) first. Methyl green 

 produces a deep green when the fibre has been previously mor- 

 danted, but light green if stained first. — Pharmaceutical Journal. 



