106 MICROSCOPICAL TECHNIQUE. 



bevelled to admit of high powers being used close to the edge, as 

 in illustration. The compressors can also be obtained thickly 

 nickelled, thus preventing tarnishing, which to some persons is so 

 objectionable. 



Filtration of Agar- Agar .■^— Dr. W. S. C. Symmers finds that 

 the ordinary methods of filtering agar-agar takes too much time. 

 He employs the method used at the Pasteur Institute. The 

 important requisite in this method is the filter-paper known as 

 " papier chardin," made by Cogit et Cie. The agar-agar is heated 

 in an autoclave to 120° C. and poured at once on to the filter- 

 paper in a cold funnel. The agar-agar filters as rapidly as nutrient 

 gelatine does in the ordinary method, and a litre may be obtained 

 in half-an-hour. 



Embedding Medium.— M. Camille Brunotte describes in the 

 Journal de Botatiique a new mode of utilising gelatine as an embed- 

 ding medium, by which the action of heat upon tissues containing 

 water can be avoided. Thin sheet gelatine, 2ogm.,is dissolved 

 by the aid of heat in 100 gm. of distilled water. The solution is 

 filtered through fine linen and 30 — 40 cm. of glacial acetic acid^ 

 and a gram of bichloride of mercury added. This addition keeps 

 the gelatine liquid at the ordinary temperature (15^ C.) and of the 

 consistence of thick syrup. To embed the material, a small 

 quantity of the liquid gelatine is poured into a little mould made 

 of thick absorbent paper (papier buvard), and the object placed in 

 it. The liquid being transparent, the position of the object by 

 immersion in water can be easily arranged. The whole is then 

 immersed in alcohol, which hardens the mass of gelatine. 



In cases in which alcohol might render cloudy the cell con- 

 tents, picric acid, bichromate of potassium, or chrome alum may 

 be used for hardening the gelatine, but these re-agents require a 

 much longer time to act. The sections, as soon as cut, can be 

 mounted in gelatine or glycerine, or can, if required, be quickly 

 freed from the thin coating of gelatine that surrounds them. 



Fixing Celloidin Sections.— Prof H. E. Summers, of Cornell 

 University (U.S.A.), recommends the following method of fixing 

 celloidin sections : — 



" The sections are first placed in 95 per cent, alcohol for a 



* British Medical Journal^ No. 1765, 1894, p. 951. 



