HISTOLOGICAL METHODS. 185 



with carmine and gelatine. Previous to this, open the com- 

 mon bile duct, so that the distension of the blood-vessels 

 may press as much of the bile out of the ducts as possible. 

 Then inject the bile capillaries from the common bile duct 

 with an aqueous solution of soluble Prussian blue. It is 

 not necessary, however, to previously inject the veins. The 

 liver of the rabbit is well adapted for injecting the bile ducts. 

 A pressure of from 0*8 to i inch mercury is usually sufficient 

 for the ducts, but it may require to be gradually increased 

 i '6 inch. The fluid being driven against the bile contained 

 in the liver, an injection of the whole liver must not be 

 attempted, but the injection should be discontinued as soon 

 as a few lobules on the surface of the liver have become 

 distinctly blue. After injection, place the liver in cold 

 methylated spirit. Mount the sections in dammar. 



METHODS OF PRESERVING THE TISSUES. 



347. The Dry Method. Hair, and sections of dried 

 bone and tooth, are sometimes mounted in air. The differ- 

 ence between the refractive powers of the tissues and the 

 air is, however, so great that the outlines are extremely 

 dark. They show better when mounted in some more re- 

 fractive medium than air, e.g. glycerine, glycerine jelly, or 

 dammar. When a tissue is mounted in air, a ring of dam- 

 mar or white zinc cement rather smaller than the cover-glass 

 is made on the slide, and allowed to nearly dry. The tissue 

 is then placed within the dammar cell (a, Fig. 62) and the 

 cover-glass placed over all and pressed upon the dammar, 

 to which it adheres. If the portion of tissue be thick, a 

 glass cell is used (b, Fig. 62). 



3 47 A. Dammar and Canada Balsam. a. All water 

 must be removed from the tissue by drying or by immer- 

 sion, first in rectified spirit and then in absolute alcohol. 

 The alcohol is driven away by floating the tissue upon oil 

 of cloves, or turpentine, in a watch glass or on a slide, and 

 then the balsam of dammar is added, and the cover-glass 

 put on (see 152). 



b. If Canada balsam be employed, prepare it as follows : 



