394 CENTRAL NERVOUS SYSTEM. 



CIAQLINSKI (Zeii. /. wis8. Mik., viii, 1, 1891, p. 22) gives the following 

 process for imbedding spinal cord : Dehydrated segments of hardened cord 

 are left for twenty-four hours in anilin oil, and then put for two or three 

 hours into xylol. They are then brought into a mixture of equal parts of 

 xylol and melted paraffin, and kept therein for twenty hours at a tempera- 

 ture of 30 C. They are then put through a twenty-four hours' bath of 

 pure paraffin to which a few drops of cedar oil have been added (said to 

 make the paraffin more elastic), the paraffin taken being of 45 C. melting- 

 point for winter work, and 52 C. for hot summer weather. Lastly, they 

 have a short bath of pure paraffin without cedar oil. 



FEIST (ibid., viii, 4, 1892, p. 492) gives a useful hint for 

 marking the right and left sides of spinal cord. He imbeds 

 with each segment of the cord a small cylinder (of about 1 

 square millimetre in section) of hardened liver, stuck verti- 

 cally in the imbedding mass (either celloidin or paraffin) 

 against the side of the cord that it is desired to mark. 



Staining. 



744. The Kinds of Stains. By a "general stain" is meant 

 one by which it is intended to demonstrate as far as possible 

 all the histological elements of a preparation. 



It does not seem possible to divide the stains used in the 

 study of the central nervous system accurately into the two 

 categories of general and special. But an incomplete division 

 is better than none at all, so I have grouped the methods as 

 general and special, meaning by the latter term those that 

 are principally intended for the demonstration of the relations 

 of nerve-fibres and ganglion-cell processes, and that make no 

 claim at all to the demonstration of other elements. 



The nuclear stains that are so important in other branches 

 of histology are here much less useful, partly because the 

 nuclei of nerve-cells happen to be remarkably poor in chro- 

 matin, and partly because the chief point of interest is not 

 the relations of nuclei, but the relations of fibres to one another 

 and to cells. 



A. General Stains. 



745. Ammonia-carmine is old-fashioned, but may be used for general 

 views. Scale's formula is a good one, especially where prolonged staining 

 is required. But in view of the greatest precision of stain, the process of 

 GIEEKE, or that of BETZ, should be preferred (see 165). 



Picro-carmine is also an excellent reagent. It has much the same action 



