CHAPTER XXV. 271 



The embryo was then fixed in Bouin's fluid, but the Prussian blue 

 faded after about a year. 



SABIN (vide infra) and CUNNINGHAM, after india-ink injection, 

 fix in Carnoy's fluid, place in 80 per cent, alcohol, dehydrate in 

 graded alcohols, clear thoroughly, first in benzine (or benzol), and 

 then in oil of wintergreen (Spalteholz). Embryos cleared by 

 Spalteholz's method may later be embedded from oil of wintergreen 

 by transferring to half wax, half oil of wintergreen, and then pure 

 wax. Tissues left in oil of wintergreen do not go brittle even after 

 a year or two (Sabin). 



For areas of osteoblastic activity, see 780, and cartilaginous 

 skeletons, 779. 



See also R. S. CUNNINGHAM (Contrib. Carng. lust. Wash., 1916, 

 No. 12) ; L. H. WEED (ibid., No. 14,1917) ; F. SABIN (Johns Hopkins 

 Hosp. Report Monographs, N.S., No. 5, Baltimore, 1913) ; Contrib. 

 to Embryol. Carneg. Inst. Wash., No. 7, 1915) ; P. G. SHIPLEY and 

 C. C. MACKLIN (Anat. Record, x, 1915-16). 



Aves. 



593. Superficial Examination. Instructions on this head are 

 given in FOSTER and BALFOUR'S Elements of Embryology. The 

 following is of more recent publication. 



If it be desired to observe a living embryo by transmitted light, 

 the egg should be opened under salt solution, as described below. 

 A little of the white is then removed through the window, the egg 

 is lifted out of the liquid, and a ring of gummed paper is placed on 

 the yolk so as to surround the embryonic area. As soon as the 

 paper adheres to the vitelline membrane, which will be in a few 

 minutes, a circular incision is made in the blastoderm outside the 

 paper ring. The egg is put back into the salt solution, and the 

 paper ring removed, carrying with it the vitelline membrane and 

 the blastoderm, which may then be brought into a watch-glass or 

 on to a slide and examined under the microscope (DuvAL). 



Gerlach's Window Method (Nature, 1836, p. 497). Remove with 

 scissors the shell from the small end of the egg ; take out a little white 

 by means of a pipette ; the blastoderm will become placed underneath 

 the window just made, and the white that has been taken out may be 

 replaced on it. Paint the margins of the window with gum mucilage, 

 and build up on the gum a little circular wall of cotton wool ; place on 

 it a small watch-glass (or circular cover-glass), and ring it with gum. 

 When the gum is dry the cover is further fixed in its place by means of 

 collodion and amber varnish, and the egg is put back in its normal 



