260 EMBRYOLOGICAL METHODS. 



of embryos ; it brings out elevations and depressions clearly, and 

 preserves admirably the mutual relations of the parts ; but it does 

 not always preserve the forms of cells faithfully, and is a hindrance 

 to staining in bulk. 



Picric liquids have an action which is the opposite of that of 

 osmic acid ; they cause cellular elements to swell somewhat, and 

 thus have a tendency to obliterate spaces that may exist in the 

 tissues. But notwithstanding this defect, the picric compounds, 

 and especially Kleinenberg's picro-sulphuric acid, are amongst the 

 best of embryological fixing agents. 



SCHKIDDE (Zeit. wiss. Mik., xxvii, 1910, p. 362) finds Orth's 

 " Formol-Muller " in general the best fixative. Fix for not more 

 than twenty-four hours, and pass through graded alcohols (twenty 

 minutes in each) into absolute (one to two hours), cedar oil, xylol, 

 and paraffin. 



RABL (Zeit. wiss. Mik., xi, 1894, p. 165) recommends for embryos 

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

 76. 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 70. 1 

 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. Wurzburg, xxxix, 1895, p. 4), in order 

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

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

 Urodela will do). SOBOTTA (Arch. mik. Anat., 1, 1897, p. 31) takes pieces 

 of amnios of Mammalia. 



SANZO (Zeit. wiss. Mik., xxi, 1904, p. 449) describes an automatic 

 apparatus for fixing material at definite stages. 



581. PETER'S Double-stain for Yolk and Tissue, see 224. 



582. 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 



