268 EMBRYOLOGICAL METHODS. 



instructive, but blacken rapidly, and cannot be permanently 

 preserved. 



The blastodermic vesicle can be opened with fine needles, and 

 the blastoderm washed, stained, or impregnated with gold, and 

 mounted in glycerin or balsam. 



For embryonic areas and more advanced embryos, refer to 

 " Cytology," 673696. KOLLIKER recommends putting the 

 ovum into 0-5 per cent, solution of osmic acid until it has taken 

 on a somewhat dark tint, which happens in about an hour, and then 

 treating it with successive alcohols for several hours. If the ovum 

 be adherent to the uterine mucosa the portion of the membrane to 

 which it is fixed should be left, stretched out with pins, in 0-1 per 

 cent, solution of osmic acid for from four to six hours. The blasto- 

 dermic vesicle can then easily be removed, and further treated as 

 before. For sections KOLLIKER fixes with osmic acid. v. BENEDEN 

 treats the ova for twenty-four hours with 1 per cent, solution of 

 chromic acid, then washes well, and brings them through successive 

 alcohols. Chromic acid has the advantage of hardening thoroughly 

 the vesicle, and maintaining at the same time the epiblast cells 

 perfectly adherent to the zona pellucida. v. BENEDEN also recom- 

 mends the liquid of Kleinenberg. HENNEGUY writes that he fre- 

 quently employs it for embryonic areas and embryos of various 

 ages, always with excellent results. Fol's modification of the 

 liquid of Flemming, and Ranvier and Vignal's osmic acid and 

 alcohol mixture ( 36) also give excellent results. For staining, 

 HENNEGUY recommends borax-carmine, or Delafield's hsematoxylin 

 for small embryos ; for large ones he found that his acetic acid 

 alum-carmine was the only reagent that would give a good stain in 

 the mass. 



For sections imbed in paraffin, or double imbed. 



590. On the Fixation of Whole Tubes. This may be done in 

 Carnoy, Bouin or Helly. For rapidity of fixation, and faithfulness 

 of preservation of cell aggregates Carnoy's fluid or preferably 

 Sansom's modification of Carnoy are to be recommended. Chrome- 

 formalin mixtures penetrate less readily, but often give fine results. 

 Bouin's fluid I have found capricious. On the whole I think that 

 warm Helly or Miiller-formol as a preliminary fixation are to be 

 recommended for small tubes. Regaud's or Schridde's methods 

 should give efficient fixation ( 684 689). Many workers have 

 used the picric mixtures like picro-sulphuric and nitric, and Kleinen- 

 berg's picric acid. Flemming's fluid has also been used. 



In later stages of development some workers open the uterus 



