142 SUMMAEY OP CURRENT RESEARCHES RELATING TO 



only be filtered with difficulty ; it also keeps a long time unchanged, 

 especially with the addition of 1-2 per cent, of chloral, and it has a 

 much more intense coloui*ing power. 



By dissolving the carmine powder in a concentrated solution of 

 neutral picrate of ammonia a combination is obtained which unites all 

 the advantages of ordinary " picrocarmine " without any of its 

 disadvantages. 



Prussian Blue and Safranine for Plant Sections.* — Prof. J. 

 Brun refers to the process of double staining for vegetable histology 

 described by him to the Geneva Physical and Natural History Society, 

 in which the action of Prussian blue alternates with that of safranine. 

 The process is to be recommended for the clearness with which the 

 preparations show all the minutest details, even in the interior of the 

 cells. The chlorophyll retains its colour, while the cellulose, the 

 layers of the cell-walls and their contents, the incrusting matter, and 

 the fatty or resinous substances are, on the contrary, differently 

 coloured and readily differentiated. He insists on the value of these 

 histo-chemical processes in distinguishing very minute transparent 

 bodies, and above all to differentiate organs scattered through opaline 

 liquids or colourless histological elements. 



Injection-Masses.t — Prof. H. Hoyer describes several compounds 

 which he has found useful for this purpose, the essential point being 

 the use of gelatine, the great objection to which is remedied by adding 

 to it chloral hydrate, which protects it from deteriorating by fungoid 

 growths. It is thus possible to have a stock of different coloured 

 masses eminently suited for injection purposes, and w^hich only 

 require to be warmed before immediate use. 



For a transparent red mass take a concentrated gelatine solution, 

 and add to it a corresponding quantity of the carmine solution 

 described supra p. 141. Digest in a water bath until the dark 

 violet-red colour begins to pass into a bright red tint. Then add 

 5-10 per cent, by volumes of glycerine and at least 2 per cent, by 

 weight of chloral in a concentrated solution. After passing through 

 flannel it can be kept in an open vessel under a bell glass. 



A hlue mass can be made by mixing a small quantity of a very 

 dilute and warm solution of Berlin blue with an equally small 

 quantity of a moderately dilute gelatine-solution, by which a clear 

 homogeneous blue solution is obtained. This is again mixed with 

 larger quantities of concentrated warm gelatine-solution, with the 

 gradual addition of now only a moderately dilute solution of Berlin 

 blue. A homogeneous transjmrent saturated mass is thus produced. 

 The addition of chloral and glycerine enables it to be kept for a 

 long time. 



For a fluid yellow in the capillaries and brown in the larger 

 vessels the following is given. A concentrated solution of gelatine 

 is mixed with an equal volume of a 4 per cent, solution of nitrate of 



* Bull. Soc. Beige Micr., viii. (1882) pp. clxix.-lxx. Journ. de Microgr., vi. 

 (1882) p. 500. 



t Biol. Centralbl., ii. (1882) pp. 19-22. 



