METHODS OF STAINING. 303 



removed by another bath of absolute alcohol, and the alcohol 

 removed by water, when the sections are ready for staining. 



It is, however, much more convenient to handle paraffin sections- 

 when they adhere to each other at their edges to form ribbons.. 

 With a paraffin microtome a little practice will enable one to secure 

 these ribbons without difficulty and of almost any desired length. 

 The ribbon may be carefully laid on the surface of perfectly clean 

 water having a temperature of 40° to 43° C, where the paraffin 

 will become softened and the ribbon will then flatten out upon the 

 water. While it is floating on the water the ribbon may be cut into 

 lengths with scissors, slides coated with Mayer's albumin mixture 

 slipped under them, and then slide and ribbon removed together 

 and drained. The slide may then be dried upon or within the 

 paraffin oven, when the sections will adhere to the glass. 



When the sections do not require affixing to slides or cover-glasses 

 they may be dropped into the solvent for the paraffin, and the latter 

 removed with absolute alcohol, for which water is then substituted, 

 preparing the sections for staining. It sometimes happens that 

 when sections are transferred from absolute alcohol to water the 

 diffusion-currents are so strong that the sections are destroyed.. 

 When this is the case the transition must be made more gradually, 

 baths of 80 per cent., 50 per cent., and 30 per cent, alcohol being^ 

 interposed between the absolute alcohol and the water. 



Methods of Staining. 



A large number of methods have been devised for bringing out 

 the structure of tissues. Many of the methods are of almost uni- 

 versal application, while others require special methods of fixa- 

 tion or other preliminary treatment of the tissues. Some are calcu- 

 lated to render the general features of structure more evident than 

 they would be if the tissues were not stained ; others stain certain 

 elements some characteristic color, and, to that extent, serve the 

 purpose of microchemical reagents. Only a few of the more useful 

 methods can be described here ; for others the reader is referred to 

 the larger text-books and the technical journals. 



Sections cut in paraffin and affixed to slides may be stained by 

 flooding the slide with the filtered dye, but it is preferable to use 

 tumblers of small diameter or Coplin jars into which the dye has 

 been filtered. The slides are then placed upright in the stain. 

 Similar vessels can also be used for the alcohol, xylol, etc., used in 



