CHAPTER XXV. 279 



607. Sulphate of Copper Liquid (FoL, Lehrbuch, p. 106, after KEMAK 

 and GOETTE) ; for hardening ova of Amphibia : 



2 per cent, solution of sulphate of copper. 50 c.c. 

 Alcohol of 25 per cent. . . . 50 ,, 



Rectified wood vinegar . . . . 35 drops. 



Pisces. 



608. Teleostea in General. The ova of many of the bony fishes 

 can be studied by transmitted light in the living state ; but those 

 of the Salmonidee must be hardened and removed from their envelopes 

 for the study of the external forms of the embryo. 



To this end they may be put for a few minutes into water con- 

 taining 1 to 2 per cent, of acetic acid, and thence into 1 per cent, 

 chromic acid. After three days the capsule of the ovum may be 

 opened at the side opposite to the embryo, and be removed with 

 fine forceps. The ovum is put for twenty-four hours into distilled 

 water, and then into successive alcohols. Embryos thus pre- 

 pared show no deformation, but the vitellus rapidly becomes 

 excessively hard and brittle, so as greatly to interfere with section- 

 cutting. 



The following processes give good results as regards section- 

 cutting. 



Put the ova for a few minutes into 1 per cent, osmic acid ; as 

 soon as they have taken on a light brown colour bring them into 

 Muller's solution. Open them therein with fine scissors the 

 vitellus, which immediately coagulates on contact with air, dissolves, 

 on the contrary, in Muller's solution and the germ and cortical 

 layer can be extracted from the capsule of the ovum. They should 

 be left in clean Muller's solution for a few days, then washed with 

 water for twenty-four hours, and brought through successive 

 alcohols. 



Another method (HENNEGUY) is as follows : The ova are fixed 

 in solution of Kleinenberg containing 10 per cent, of acetic acid. 

 After ten minutes they are opened in water containing 10 per 

 cent, of acetic acid, which dissolves the vitellus. The embryos 

 are put for a few hours into pure solution of Kleinenberg, 

 and are then brought through alcohol of gradually increasing 

 strength. 



CHILD (quoted from SUMNER, Mem. New York Acad. Sci., ii, 

 1900, p. 78) fixes for about a minute in sublimate with 10 per cent, 

 of acetic acid, and brings into formalin of 10 per cent., which is 

 said to give a good fixation of the embryo without the yolk becoming 

 hard. 



