Method IX 57 



It must be remembered that all the elements of a piece of 

 tissue are never blackened in the same preparation by the Golgi 

 method. Far from being a defect, this is of great advantage. 

 If all the elements were to stain at one time, it would be 

 extremely difficult to discriminate one from another or to decide 

 the extent of any one, owing, to the dense interweaving of their 

 branches. 



Also it is an advantage at times that the same structures are 

 not always brought out. In some preparations it may be the 

 neuroglia cells almost alone ; in others, the cell-body of the 

 neurone or the axone chiefly; while in still others it may be that 

 only the vessels are stained. The latter, however, is but too 

 often the case. 



Fcetal material, by either modification, is generally more 

 fortunate for the peripheral ganglia or for the Purkinje cells of 

 the cerebellum. 



THE RAPID METHOD. 



1. To fix. — From the chloroformed animal or from the fresh 

 fcEtus carefully remove pieces of the tissue required (not 

 thicker than 5 mm.), place them in about 30 times their volume 

 of the osmium-bichromate mixture (A, i), and set aside, prefer- 

 ably in the dark, for 12-24 hours. 



2. Replace the fixing fluid with an equal quantity of the 3.5 

 per cent, potassium bichromate solution (B) for 3 days or more. 

 The length of time required in this fluid is thought to vary for 

 the different structures : neuroglia, 2-3 days ; cortical cells, 

 3-4 days ; Purkinje, spinal cord, and peripheral ganglion cells, 

 4-5 days ; and for the nerve-fibers of the spinal cord, 5-7 days. 



3. To impregnate. — Remove the surplus bichromate by placing 

 the pieces of tissue on filter paper, then place them in a clean 

 vessel, and agitate a small amount of the silver nitrate solution 

 (C) about them till the brown precipitate of silver chromate no 

 longer appears in the fluid, and then place them in about 30 

 times their bulk of fresh silver nitrate solution for 3 days or 

 more. 



It is thought best to keep the vessel in the dark during this 



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