380 SOME ZOOLOGICAL METHODS. 



Journ. Roy. Mic. Soc. t 1885, p. 538). Fix for a few minutes 

 with -J- per cent, aqueous solution of chloride of palladium. 

 This is the best fixing agent, as it hardens in a few minutes 

 without blackening the structures. Double chloride of gold 

 and cadmium also fixes well, and brings out nuclei even better 

 than the palladium. Solution of iodide of mercury and potash 

 (i per cent.) is useful for bringing out protoplasmic networks, 

 as it stains the granules of protoplasm black. Corrosive sub- 

 limate in 5 per cent, solution gives good results. Osmic acid 

 causes darkness and opacity in the preparations. Nitrate of 

 silver (in 4 to 1 per cent.) solution may be used, the objects 

 being washed out with solution of acid sulphate of soda. 

 Chromic, picric, and picro-sulphuric acids and bichromate of 

 potash are only second-rate fixing agents for this purpose. 



The best stains are carmine and picro-carmine. Magenta- 

 red and fuchsin both give good results ; nigrosin and heema- 

 toxylin (Kleinenberg's) still better. These should be used in 

 weak solutions and allowed to act for a long time. 



756. BRASS (Zeit. f. wiss. Mik., 1, 1884, p. 39) employs for 

 fixing unicellular organisms the following liquid : 



Chromic acid . . . . .1 part. 

 Platinum chloride . . . 1 



Acetic acid . . . . . 1 



Water . . . . 400 to 1000 

 For protozoa that are opaque through accumulation of 

 nutritive material, he proceeds as follows : The organisms are 

 treated for three or four minutes with liquid of Kleinenberg, 

 and then for some time with boiling water. They are then 

 brought into water containing a small proportion of ammonia, 

 in which they reassurne their natural forms and dimensions. 

 The ammonia is then neutralised by addition of a little acetic 

 acid, and the preparation is stained with borax carmine or 

 ammonia carmine. After washing, the objects are mounted 

 in dilute glycerin. This treatment is said to afford extremely 

 transparent preparations. 



Brass also obtained good results with sublimate solution. 



757. CEKTES (Comptes rend., 1879, 1 sem., p. 433) makes 

 permanent preparations as follows : Fix with osmic acid of 

 2 per cent. (In the case of very contractile Infusoria, place a 

 drop of the solution on the cover-glass, and place it on the 



