EMBBIOLOGICAL METHODS. 289 



Rabl (Zeit. wiss. Mik., xi, 1894^ p. 165) recommends for 

 embryos of VertebrateSj and also for other objects^ his platinic 

 sublimate, § 76. This serves for a large number of blasto- 

 derms and young embryos (Pisces, Amphibia, Aves, Mam- 

 malia). Advanced embryos of Teleostea ought to be fixed 

 in the warmed mixture, in order to avoid rupture of the 

 muscles and shrinkage of the chorda. 



Some of his best results were obtained by a not too pi'o- 

 longed fixation in a mixture of 



Platinic chloride, 1 per cent, solution . 1 vol. 

 Picric acid, saturated aqueous . . 2 vols 



Distilled water . . . . . 7 „ 



Rabl's picro-sublimate mixture has been given § 70. It 

 is recommended especially for somewhat advanced embryos, 

 such as embryo chicks from the third or fourth day, and 

 other embryos of a similar size. 



BovERi iVerh. Phys. Med. Ges. Wiirzburg, xxxix, 1896, p. 4), in order to 

 imbed and cut together numbers of ova of Echinoderms, wraps them in 

 pieces of sloughed epidermis of Cryptobranchits (of course, other Urodela 

 will do). SoBOTTA {Arch. mik. Anat., 1, 1897, p. 31) takes pieces of 

 amnios of Mammalia. 



Sanzo {Zeit. wiss. Mile, xxi, 1904, p. 449) describes an automatic 

 apparatus for fixing material at definite stages. 



588. Petee's Double-stain for Yolk and Tissue, see § 224. 



589. Removal of Albumen. — The thick layers of albumen 

 that surround many ova are a serious obstacle to the penetra- 

 tion of reagents. Child [Arch. Entwichelungsmech. , ix, 1900, 

 p. 587) gives the following as of very general applicability. 

 After fixation (in any way except with chromic acid) the ova 

 are brought through graduated alcohols up to that of 80 

 per cent., in which they are hardened. They are then 

 brought down again through successive alcohols into water 

 acidified lightly with any acid (except chromic acid), and the 

 albumen is found to become transparent and dissolve. 



590. Reconstruction of Embryos from Sections. — To facilitate 

 the study of series of sections, recourse may be had to 

 graphic or plastic reconstruction of the objects. 



In simple cases it may be sufficient to adopt the plan 



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