MICROSCOPICAL TECHNIQUE 



91 



To Stain Wood Black.— A process that is much employed for 

 the above purpose consists in painting the wood consecutively 

 with copper sulphate solution (i per cent.) and alcoholic aniline 

 acetate (equal parts of alcohol and acetate). A very durable 

 black, and the nearest approach to real ebony, is readily obtained 

 by moistening the surface of the wood with dilute sulphuric acid 

 (i : 20), and subsequently applying heat. A temperature of 60° 

 to 90^ C. suffices in a very few minutes to produce the desired 

 result. An excellent black was obtained in this way on beech, 

 bass, and boxwood ; while a second treatment was necessary in 

 the case of cherry, walnut, and birch. With oak and ash the 

 results were not so good ; and apple and different varieties of pine 

 were still less amenable to the process, pine especially being 

 unevenly stained. In order to afterwards remove the acid from 

 the wood, it might be well to thoroughly wash the latter with dilute 

 soda solution, followed by clean water. It is unlikely that this 

 method can be applied to any but small articles, because of the 

 risk of possible fractures during the necessary heating of the wood. 

 — Boston Jour7ial of ChetJiistry. 



Preservation of Microscopic Specimens.— Tores (Cent./, allg. 

 Path u. Path. Atiat) (1896, p. 134) describes a method which he 

 has tested for a year and a-half, of preserving organs and tissues 

 so that they retain the colour they had when fresh. He finds 

 that 5 to 10 parts of a 40 per cent, solution of formalin alone, 

 causes the organs after a time to assume a tint which differs very 

 considerably from the natural colour ; but that if instead of water 

 for diluting the commercial formalin solution, a solution of i part 

 common salt, 2 parts of magnesium sulphate, 2 parts sodium 

 sulphate, in 100 parts of water be used, the colour of the blood 

 is well preserved. Further, material preserved in such a solution 

 is better adapted for subsequent microscopic examination, since 

 the protoplasm of the cell is less altered, and the nucleus stains 

 better and more deeply. 



The method he adopted is as follows : The material must not 

 be too long washed in water, and should be left in the lornialin 

 solution for a period depending on their size and thickness. A 

 kidney or spleen requires two days' immersion, and the solution 



