350 CHAPTER XXVI. 



624. Removal of Membranes. This is frequently very diffi- 

 cult, and it may often be advisable not to attempt to remove 

 them, but to soften them with eau de Javelle or eau de Labar- 

 raque (see 556). 



MOBGAN (Amer. Natural., xxii, 1888, p. 357 ; Zeit. f. u-iss. 

 Mik., vi, 1, 1889, p. 69) recommends (for the ova of Peri- 

 planeta] eau de Labarraque diluted with five to eight volumes 

 of water, and slightly warmed. Thus used it will soften the 

 chitin membranes sufficiently in thirty to sixty minutes, if 

 employed before fixing. Fixed ova take longer. The fluid 

 must, of course, not be allowed to penetrate into the interior 

 of the ovum. 



625. HENKING'S Methods (Zeit. f. wiss. Mik., viii, 2, 1891, 

 p. 156). HENKING generally kills ova by plunging them into 

 hot water, or by pouring hot water on to them in a watch 

 glass, and then removing into 70 per cent, alcohol. But he 

 finds that the preservation of structures by this method is 

 far from being perfectly satisfactory, cell contours being not 

 at all sharply brought out by it, and achromatic cell structures 

 being but imperfectly preserved. He finds that in some cases 

 ova may be fixed with liquid of Flemining, which then gives 

 incomparably better results in these respects. Suitable ova 

 may be put into liquid of Flemming (HENKING does not say 

 which formula) for half an hour, then for two hours into the 

 same diluted with three volumes of water, then treated with 

 alcohol as usual. BOVERI'S picro-acetic acid was found not 

 to penetrate the membranes. 



HENKING thinks that eau de Javelle for softening mem- 

 branes is best avoided. They should either be dissected 

 away or left in situ, and cut with the rest of the egg, accord- 

 ing to the nature of the case. The great obstacle to section- 

 cutting is the brittleness of the yolk. This difficulty may be 

 overcome as follows : After fixing and treating with alcohol, 

 prick the chorion and stain with borax-carmine. Put the 

 stained ova for twelve hours into a mixture containing 

 20 c.c. of 70 per cent, alcohol, one drop of concentrated 

 hydrochloric acid, and a knife pointful of pepsin (it is not 

 necessary that all the pepsin should be dissolved). The ova 

 may then be treated with alcohol, oil of bergamot, and 



