NITRIC ACID. 287 



mended by HOPKINS in the same place. A few hours' macera- 

 tion is generally sufficient. 



541. Osmic Acid. Ol per cent., for from a few minutes to 

 a fortnight (cortex of cerebrum Kindfleisch) . Maybe fol- 

 lowed by maceration in glycerin. 



542. Osmic and Acetic Acid (the HERTWIGS' Liquid, Das Ner- 

 vensystem u. die Sinnesorgane der Medusen, Leipzig, 1878, and~ 

 Jen. Zeitschr., xiii, 1879, p. 457 ; Journ. Roy. Hie. Soc.j iii, 

 1880, p. 441, and [N.S.] iii, 1883, p. 732). 



0'05 per cent, osmic acid . . .1 part. 



0'2 acetic acid . . . 1 

 Medusae are to be treated with this mixture for two or 

 three minutes, according to size, and then washed in repeated 

 changes of 0*1 per cent, acetic acid until all traces of free 

 osmic acid are removed; they then remain for a day in 0*1 

 per cent, acetic acid, are washed in water, stained in Beale's 

 carmine (in order to prevent the osmium from over- blacken- 

 ing, and to assist the maceration), and are preserved in 

 glycerin. 



For Actinise, the osmic acid is taken weaker, O04 per cent. ; 

 both the solutions are made with sea water; and the washing 

 out is done with 0*2 per cent, acetic acid. If the maceration 

 is complete, stain with picro-carmine ; if not, with Beale's 

 carmine. 



543. BELA HALLER'S Mixture (Morphol. Jahrb., xi, p. 321). 

 One part glacial acetic acid, 1 part glycerin, 2 parts water. 

 Specially recommended for the central nervous system of 

 Mollusca (Rhipidoglossa), A sufficient degree of macera- 

 tion is obtained in thirty to forty minutes, the cells showing 

 less shrinkage than with other liquids. 



544. Nitric Acid. Most useful for the maceration of muscle. 

 The strength used is 20 per cent. After twenty-four hours' 

 maceration in this, isolated muscle-fibres may generally be 

 obtained by shaking the tissue with water in a test-tube. 

 Preparations may afterwards be washed with water and put 

 up in strong solution of alum, in which they may be preserved 

 'for a long time ( HOPKINS, Proc. Amer. Soc. of Microscopists, 



1890, p. 165 ; Zeit. f. wlss. Mik., ix/1, 1892, p. 86). 



Maceration is greatly aided by heat, and at a temperature 



