CHAPTER XXV. 265 



is desired to study these the animal may bo killed, or may be subjected 

 to a secondary laparotomy if it be desired to preserve it for ulterior 

 observations. This method, however, cannot be carried out in this 

 country owing to the Vivisection Acts. 



This procedure was also adopted by Hartmann in his study on 

 Didelphys (vide infra). 



586. Fixation of the Isolated Ova. These can be fixed in a chrome- 

 formalin fluid of some kind : Muller-formol, Helly, Zenker- without- 

 acetic acid and formol are indicated. Eggs may be left in one of 

 these fluids overnight, then washed in distilled water and transferred 

 either to 1 per cent. Os0 4 , or to some chrome-osmic fluid, this to 

 preserve the fat. The chrome fixation will form insoluble compounds 

 with lipoids, but less so with fats of the type of olein. It seems 

 likely that the fixation technique of Champy-Kull, of Schridde and 

 of Murray (see 689) will be of great value. 



For a study of the Golgi elements the methods of Cajal and 

 Da Fano and of Mann-Kopsch are worthy of trial, but rather more 

 difficult to work than chrome-osmic or chrome-formol techniques. 

 Where there may be a difficulty of penetration chrome-formol 

 fluids will be found better than chrome-osmium. A perusal of the 

 sections on Mitochondria and Golgi apparatus will provide sugges- 

 tions for the treatment of the early stages in mammalian develop- 

 ment. VAN BENEDEN (Arch, de Biol, 1880, p. 149) brings the living 

 ovum into a drop of 1 per cent. Os04 on a slide, and thence into a 

 solution of Miiller. After an hour the liquid is changed, and the 

 whole is put into a moist chamber, where it remains for two or 

 three days. It is then treated with glycerine of gradually increasing 

 strength, and at last mounted in pure glycerine acidified with formic 

 acid. I am inclined to believe that the Champy-Kull or Regaud 

 fixation (the latter with a post-osmication) would be much superior 

 to the above method, that is, for sectioning. 



Many authors have used picro-nitric, picro-sulphuric, picro- 

 formol with or without corrosive, chromic-acetic acid, Flemming 

 and Hermann, and so on, but one cannot help thinking that the 

 more modern and logical fixation methods will be better. This 

 seems borne out by the late work of LAMS (Arch, de Biol., t., xxiii), 

 and LEVI (Arch.f. Zellf., xiv). 



J. P. HILL (Quart. Jour. Micr. Soc., 1910) gives the formula of 

 a " Marsupial mixture " for fixation of ova and blastocysts of Mar- 

 supials. This fluid is made by adding to 96 c.c. of Mayer's picro- 

 nitric, 2 c.c. of 1 per cent. Os0 4 . Two c.c. of glacial acetic acid 

 may be added, but the picric acid is sufficiently penetrative without 

 the addition of acetic acid. 



