EMBRYOLOGY 361 



Rabl {Zeit. zviss. Mik., xi, 1894, p. 165) recommends for 

 embryos of Vertebrates, and also for other objects, his platinic 

 sublimate, § 81. This serves for a large number of blastoderms 

 and young embryos (Pisces, Amphibia, Aves, Mammalia). 

 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 prolonged 

 fixation in a mixture of 



Platinic chloride, 1 per cent, solution 1 volume. 

 Picric acid, saturated aqueous . 2 volumes. 



Distilled water . . . .7 ,, 



Rabl's picro-sublimate mixture has been given, § 75. 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 (Verh. Phys. Med. Ges. Wurzhnrg, xxxix, 1895, p. 4), in order 

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

 in pieces of sloughed epidermis of Cryptohranchus (of course, other 

 Urodela will do). Sobotta {Arch. mik. Anat., 1, 1897, p. 31) takes pieces 

 of amnion of Mammalia. 



Sanzo {Zeit. iviss. Mik., xxi, 1904, p. 449) describes an automatic 

 apparatus for fixing material at definite stages. 



799. Removal of Albumen. The thick layers of albumen that 

 surround many ova are a serious obstacle to the penetration of 

 reagents. Child {Arch. Entwickelungsmech., 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. 



800. 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 described 

 by ScHAFFER {Zeit. wiss. Mik., vii, 1890, p. 342). Careful outlines 

 of the sections to be constructed are drawn on tracing paper with 

 the aid of the camera lucida, superposed, and held up against the 

 light for examination by transparence. Vosmaer {Anal. Anz., 

 xvi, 1899, p. 269) draws on plates of celluloid, and sets them up 

 in a rack for examination. Kerr {Quart. Joiirn. Mic. Sci. xlv, 

 1902, p. 1) draws on plates of ground glass which he afterwards 

 superposes and makes transparent by oil of cloves run in between 

 them. Pensa {Zeit. wiss. Mikr., xxvii, 1910, p. 48) takes sheets 



