336 CHAPTER XXVI. 



living ovum may be brought into one third per cent, solution 

 of nitrate of silver. After remaining there for half a minute 

 to two minutes, according to the age of the vesicle, it is 

 brought into pure water and exposed to the light. The pre- 

 parations thus obtained are instructive, but blacken rapidly, 

 and cannot be permanently preserved. 



After the end of the third day the blastodermic vesicle 

 can be opened with fine needles, and the blastoderm washed, 

 stained, and mounted in glycerin or balsam ; v. BENEDEN 

 has also obtained good preparations by means of chloride of 

 gold. 



For embryonic areas and more advanced embryos 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 O'l 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 recommends 

 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 modifica- 

 tion of the liquid of Flemming, and Ranvier and Vignal's 

 osmic acid and alcohol mixture ( 39 A) also give excellent 

 results. For staining, HENNEGDY recommends borax -carmine, 

 or Delafield's haematoxylin 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. I think 

 carmalum is now indicated. 



For sections imbed in paraffin. 



See also WEYSSE, Proc. Amer. Acad. Arts and Sci., 1894, 

 p. 285 (blastodermic vesicle of Sus scrofa) ; SOBOTTA, Arch, 

 f. mik. Anat., xlv, 1895, p. 15 (fecundation and segmentation 



