38 HISTOLOGIC.\L TECHNIC 



Golgi specimens should be dehydrated and embedded as rapidly 

 as possible. This is especially true of specimens treated by the rapid 

 and the mixed methods. Those treated by the slow silver method 

 and by the bichlorid method are more permanent, and more time may 

 be taken with their dehydration. Thick sections should be cut (75 

 to ioo/() and mounted in xylol-balsam. After the rapid method; it is 

 safer to mount without a cover-glass; after the slow method, speci- 

 mens may be mounted with or without a cover. The balsam should 

 be hard, and melted at the time of using. (See Mounting, page 22.) 



Cajal's Methods for Staining the Neurofibrils in the 



Nerve-cells 



In these methods, besides the neurofibrils, the cell processes and 

 especially the axis cylinders are often beautifully displayed, the stain 

 giving a picture in this respect much more general than that of the 

 Golgi methods, but much more specific, and sharper than that of the 

 ordinary stains. 



The methods consist mainly of two steps: (i) The staining of the 

 tissue in a solution of silver nitrate; (2) the further reduction of the 

 silver stain with a weak photographic developer. Three methods, 

 or variations, are here given: 



(i) Pieces about 0.5 cm. thick are placed in a liberal quantity of 

 from i-per-cent. or 1.5-per-cent. (new-born or embryonic mammalian 

 material) to 5-per-cent. (adult material) solution of silver nitrate and 

 kept at a temperature of 32° to 40° C. for two to five days. When 

 properly stained (shown by a yellowish or light brown coloration of 

 freshly cut surfaces) the pieces are very briefly rinsed in distilled 

 water and placed in: pyrogallol (or hydroquinone) i gm., distilled 

 water 100 c.c, formalin 5 to 10 c.c, for twenty-four hours or more. 

 They are then washed a few minutes in water and transferred to 

 95-per-cent. alcohol, which is changed when discolored, and where 

 they may often be kept for some time without injury. They may 

 then be embedded in celloidin or paraffin and sections cut, usually 

 15-25/i in thickness. Difi'erent depths of the blocks of tissue usually 

 vary in stain, the most favorable being intermediate between the 

 surface and centre of the block. Celloidin sections usually keep well 

 in 95-per-cent. alcohol. They may be cleared in carbol-xylol, 

 rinsed in xylol, and mounted in xylol-balsam or xylol-damar in 

 the usual way." In dehcate objects (study of pathological changes 



