CHAPTER XXV. 277 



the inner chorion with fine scissors or needles, and gently press out 

 the ovum. Harden in alcohol. 



FICK (Zeit. wiss. Zool., Ivi, 1893, p. 529) uses a mixture of 250 parts 

 of 1 per cent, chromic acid, 1 of acetic acid, and 750 of water. 



604. Triton (ScoTT and OSBORN, Quart. Journ. Mic. Soc., 1879, 

 p. 449). The albumen is here present in the form of several con- 

 centric coats, which are very delicate. Incise each of them separately 

 with fine scissors, turn out the ovum, and fix it in solution of 

 Kleinenberg. 



HERTWIG (Jen. Zeit. Naturw., 1881 2, p. 291) puts the eggs 

 into a mixture of equal parts of 2 per cent, acetic acid and 0-5 per 

 cent, chromic acid. After ten hours he incises the membranes, 

 opening one end of the inner chorion, and turns out the embryos 

 and brings them into successive alcohols. 



MICHAELIS (Arch. mik. Anat., xlviii, 1896, p. 528) fixes ova, 

 with their envelopes, in a mixture of concentrated sublimate solution 

 and concentrated picric acid, 20 parts each, glacial acetic acid 1, 

 and water 40, but removes the envelopes before bringing into 

 alcohol. 



605. Salamandra (RABL, Morphol. Jahrb., xii, 2, 1886, p. 252).- 

 For his more recent methods see 580. 



GRONROSS (Anat. Anz., xiv, 1898, p. 461) fixes the ova with a 

 mixture of 50 parts each of saturated sublimate and 0-5 per cent, 

 chromic acid with 1 part of acetic acid. 



606. Rana. I have found that the following mixture often gives 

 very good results for the eggs of Rana temporaria ; it dissolves 

 away the albumen coat, preserves yolk and mitochondria, and 

 leaves the eggs soft enough to cut in paraffin with a rotary micro- 

 tome : 



Bichromate of potash of 2 per cent. . 100 c.c. 

 Chromic acid of 1 per cent. . . . 100 

 Nitric acid . . . . . 6 



Use at least 40 c.c. to twenty or thirty eggs for fifteen to twenty- 

 four hours. Slightly shake, and the albumen coats fall off if not 

 already dissolved. Wash out for about one hour in running water 

 and then upgrade from 70 per cent, alcohol (one half-hour), 90 per 

 cent, (one hour), to absolute alcohol, two changes of one hour each. 

 Clear in benzol for fifteen minutes. Add chips of wax and place in 

 thermostat for half an hour. Transfer to pure wax for one-half 

 (to three-quarters) of an hour. Avoid unnecessary heat. 



