IODINE. 41 



and the operation is repeated until the fresh cupric sulphate no longer 

 becomes conspicuously blue on contact with the alcohol ; or until, on a drop 

 of the alcohol being mixed with a drop of turpentine, no particles of water 

 can be seen in it under the microscope. The cupric sulphate is prepared by 

 calcining common blue vitriol in a porcelain capsule over a spirit lamp or 

 gas burner until it becomes white, and then reducing it to powder (see 

 Proc. Acad. Nat. Sci. Philad., 1884, p. 27 ; Science Record, ii, 1884, p. 65 ; 

 Journ. Roy. Micr. Soc., (N.S.), iv (1884) pp. 322 and 984). 



63. Acidulated Alcohol (PAUL MAYER, Mitth. Zool. Stat. Neapel, ii 

 (1881), p. 7. To 97 vols. of 90 per cent, alcohol, in which is dissolved a 

 small quantity of picric acid, add 3 vols. pure hydrochloric acid. Leave the 

 specimens in the mixture only just long enough to ensure that they are 

 thoroughly penetrated by it. Wash out with 90 per cent, alcohol, the dis- 

 appearance of the yellow stain of the picric acid being a sign that all the 

 acid is removed. 



The use of this mixture is for the preparation of coarse objects it is intended 

 to preserve in alcohol. The object of the acid is to prevent both that glueing 

 together of organs by the perivisceral liquid, which is often brought about 

 by the coagulating action of pure alcohol, and the precipitation on the surface 

 of organs of the salts contained in sea- water, which is a hindrance not only 

 to the penetration of the alcohol, but also to subsequent staining. 



Whitman (Journ. Roy. Mic. Soc. (N.S.), ii (1882), p. 870) states that 

 " acid alcohol as above prepared loses its original qualities after standing 

 some time, as ether compounds are gradually formed at the expense of the 

 acid." He also states that 70 per cent, alcohol may be taken instead of 90 

 per cent., for washing out. 



64. Chloride and Acetate of Copper (Ripart et Petit's formula, 

 CABNOY, La Biologie Cellulaire, p. 94). 



Camphor water (not saturated) . . 75 grammes. 



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. I consider that it has not 

 sufficient hardening power for objects that are intended to be dehydrated 

 and mounted in balsam, but is frequently excellent and sometimes indis- 

 pensable 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 this is a most invaluable medium. 



65. Acetate of Uranium (SCHENK, Mitth. a. d. Embryol. Inst. Wien, 

 1882, p. 95 ; cf. GILSON, La Cellule, 1, 1885, p. 141). This reagent is very 

 similar in its properties to picric acid. It has a mild fixing action, and a high 

 degree of penetration, which may make it useful for Arthropoda. It may be 

 combined with methyl green, which it does not precipitate. 



66. Iodine. Iodine possesses considerable hardening properties, and a 



