374 EMBRYOLOGY 



may be restored by treating the sections on the slide for twenty- 

 four hours with strong Flemming. From 60 per cent, alcohol 

 stain in a ^ per cent, to 1 per cent, solution in 50 per cent, alcohol 

 for twenty-four hoiu's. Wash in several changes of distilled 

 water, and then place in 1 per cent, aqueous gentian violet for 

 twenty-four hours. Wash in aq. dest. Stain in aqueous solution 

 of orange G for from some seconds to one minute. The orange 

 G solution should be from 1 in 500 to 1 in 1000 in aq. dest. strength, 

 varying according to the object, embryonic material needing the 

 stronger solution. Finally treat sections with acidulated alcohol 

 for a few seconds : on the first cloud of violet appearing, transfer 

 to absolute alcohol. Transfer to oil of cloves containing a little 

 absolute alcohol. Control differentiation under microscope. Then 

 treat with pure oil, drain off, finally wash with xylol and mount in 

 balsam. 



815. Held's Molybdic Acid Haematoxylin. To a 1 per cent, 

 solution of haeinatoxylin in 70 per cent, alcohol, add sufficient 

 molybdic acid to form a layer on the bottom of the bottle. Shake 

 frequently. After fourteen days, there is noticeable alteration in 

 colour to deep blue-black. Solutions from months to one or two 

 years' old stain best. Pour off the stain from the deposit, and 

 just before use add some drops to some distilled water to make a 

 semi-transparent solution. Stain at 50° C, or in cold up to twelve 

 hours or more. Examination of the sections will reveal whether 

 the stain is sufficient. W^ash in water, and upgrade. 



Alternatively, the sections may be mordanted in iron alum, 



Overstained sections may be differentiated in 5 per cent, iron 

 alum. Such fixatives as Zenker are suitable for this stain, but 

 it may be used with almost any material. It is particularly good 

 for nerve tissues during development. 



For areas of osteoblastic activity, see § 921, and cartilaginous 

 skeletons, § 923, 



See also R, S, Cunningham {Contrib. Carng. Inst. 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 



816. 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 



