PREPARATION AND STAINING OF TISSUE SECTIONS. 57 



the knife with a clean needle, and dropped into a 

 watch-glass containing xylol. This dissolves out 

 the paraffin ; the sections are then transferred to 

 alcohol to get rid of the xylol, and then to the 

 staining solution. 



In the case of specimens embedded in celloidin, 

 or mounted directly on a cork, the tissue, as well as 

 the blade of the knife, should be kept constantly 

 bathed with alcohol, and the sections transferred 

 from the blade with a camel's hair brush, and 

 floated in alcohol. 



For fixing small organs and pieces of firm tissue 

 directly on cork, such as the kidneys of a mouse, 

 or liver, one employs gelatine, or glycerine-gelatine, 

 liquefied over a Bunsen burner in a porcelain cap- 

 sule. The cork with specimen affixed is placed in 

 alcohol, and is ready for cutting sections next day. 



The advantage of glycerine-gelatine consists in 

 that it may be used for fixing irregular pieces of 

 tissue, as it does not become of a consistency that 

 would injure the edge of the knife. 



(c) GENERAL PRINCIPLES OF STAINING BACTERIA 



IN TISSUE SECTIONS: METHODS OF WEIGERT, 

 GRAM, AND WEIGERT-EHRLICH. 



Sections of fresh tissues made with the freezing 

 microtome are to be floated and well spread out 

 in *8 per cent, salt solution, and then carefully 

 transferred, well spread out on the copper lifter, to 

 a watch-glass containing absolute alcohol. Simi- 



