570 TEXT-BOOK OF EMBRYOLOGY. 



Another in toto silver method is that of Bielschowsky, modified by Paton. This method 

 is more complicated, as is also Bielschowsky's important method of staining sections. 



None of the silver methods has an absolutely reliable technic, especially for embryological 

 work. They are particularly designed to bring out the neurofibrils which are often sharply 

 and deeply stained. The non-neurofibrillar portions of the cell-body and its processes are 

 also often, especially in the adult, clearly defined though not so deeply stained. The 

 picture is thus a more general one than that yielded by the methods of Golgi and reveals 

 important details of internal cell structure. It is, however, inferior to the Golgi methods in 

 displaying the finest ramifications of the processes. 



Weigert's Method. — For studying myelination, the method of Weigert or one of its 

 modifications is used. The specimen is fixed and hardened in Muller's fluid, or preferably 

 fixed for two or three days in Muller's fluid 9 vols., formalin 1 vol. (the fluid being changed 

 once or twice), and then hardened for three or four weeks in Muller's fluid. After a short 

 washing in water the specimen is carried through graded alcohols, the alcohol being changed 

 until the bichromate no longer colors it. If the specimen is kept in the dark, precipitation 

 of the bichromate is avoided. The specimen is embedded in celloidin or paraffin and 

 sectioned in the usual way. 



In the unmodified Weigert method, the sections are carried from water into a saturated 

 or half saturated aqueous solution of neutral cupric acetate for twelve to twenty-four hours. 

 They are then rinsed in water until the free cupric acetate is removed, and transferred to a 

 mixture of 9 vols, of No. 1 solution and 1 vol. of No. 2. 



No. 1. Water, IO o c.c. 



Saturated aqueous solution lithium carbonate, 1 or 2 c.c. 

 No. 2. Hematoxylin, 10 grams. 



Alcohol, 95 per cent, or absolute, 100 c.c. 



Solution No. 2 should be a week or more old. Sections should remain in the above mix- 

 ture for from twelve to twenty-four hours and are then differentiated in the following- 

 Potassium ferricyanide, 21/2 grams. 



Borax, 2 grams. 



\\ ater, 100 c.c. 



After differentiation is complete, the specimens should be washed for half an hour or more 

 in water, dehydrated, cleared in carbol-xylol and xylol, and mounted in xylol-damar or 

 balsam. 



The most important modification of Weigert's method is the so-called Weigert-Pal method. 

 This method should be used only with celloidin sections. The sections are transferred 

 directly into either a 10 per cent, solution of hasmatoxylin in alcohol, 1 vol. + water, 9 vols., or 

 into 1 vol. of the hematoxylin solution + 9 vols, of a 1 per cent, or 2 per cent, solution' of 

 acetic acid. 



If the material has been kept in alcohol for some time, it may be advisable, before staining, 

 to mordant for from one to several days in 5 per cent, potassium bichromate or in Muller's 

 fluid. Copper bichromate, • per cent, to 3 per cent. (12 hours), is a stronger mordant, but 

 may make the sections' brittle. 



When stained, the sections are rinsed in water and differentiated as follows- First place 

 m a freshly made 1/5 per cent, to x/ 3 per cent, solution of potassium permanganate, 

 usually about 1/2 minute, then rinse in water and transfer to 



Potassium sulphite r gram. 



Oxalic acid, j gram 



Water, 200 cc _ 



