CHLORIDES ORGANIC ACIDS ETC. 51 



95. Chloride and Acetate of Copper (Ripart ct Petit" s Liquid, Carnoy, 

 La Biologic Cellulaire, p. 94). 



Camphor water (not saturated) . 75 grm. 



Distilled water . . . . 75 ,, 



Crystallised acetic acid . . 1 ,, 



Acetate of copper . . . 0-30 „ 



Chloride of copper . . . 0-30 ,, 



This is a very moderate and delicate fixative, extremely useful for 

 objects that are to be studied in as fresh a state as possible in aqueous 

 media. Objects fixed in it stain instantaneously and perfectly with 

 methyl green. Osmic acid may be added to the liquid to increase 

 the fixing action. For cytological researches a valuable medium. 



96. Nitrate of Copper (Gilson, from Gelderd, La Cellule, xxv, 

 1909, p. 12). Nitrate of. copper 200 c.c. sat. sol., formol 500 c.c, sea- 

 water 200 c.c. Seven parts of this solution to be diluted with 100 of 

 sea-water. For Crustacea. 



97. Acetate of Uranium (Schenk, Mitth. Embryol. Inst. Wicn, 1882, 

 p. 95 ; cf. Gilson, La Cellule, i, 1885, p. 141) has a mild fixing action, 

 and a high degree of penetration, and may be combined with methyl 

 green . 



Friedenthal (Sitzb. Ges. Nat. Freunde Berlin, 1907, p. 209) recom- 

 mends equal parts of saturated solution of the acetate and trichlor- 

 acetic acid of 50 per cent. 



98. Picric Acid. Picric acid in aqueous solution should be 

 employed in the form of a strong solution whenever it is desired to 

 make sections or other preparations of tissues with the elements 

 in situ, as weak solutions macerate ; but for dissociation pre- 

 parations or the fixation of isolated cells, weak solutions may be 

 taken. Flemming found that the fixation of nuclear figures is 

 equally good with strong or weak solutions. The saturated 

 solution is the one most employed. (One part of picric acid 

 dissolves in about 86 parts of water at 15° C. ; in hot water it is 

 very much more soluble.) Objects should remain in it for from a 

 few seconds to twenty-four hours, according to their size. For 

 Infusoria one to at most two minutes will suffice, whilst objects of 

 a thickness of several millimetres require several hours. 



Picric acid should always be washed out ivith alcohol, that of 

 70 per cent, being mostly indicated. Staining is better performed 

 by means of alcoholic solutions, or if with aqueous, then with 

 such as are themselves weak hardening agents, such as hsemalum, 

 carmalum, methyl green. 



Washing out is facilitated by heat, the extraction being about 

 twice as rapid at 40° C. as at the normal temperature (Fol). 



It has been found by Jelinek {Zeit. wiss Mik., xi, 1894, p. 242) 

 that the extraction is greatly quickened by the addition of a base 

 to the wash-alcohol. He recommends carbonate of lithium. A 

 few drops of a saturated solution of the salt in water are added to 

 the alcohol ; a precipitate is formed. The objects are put into 

 the turbid alcohol, which becomes clear and yellow in proportion 

 as the picric is extracted. Further quantities of carbonate are 



