METHODS OF IMPREGNATION. 



47 



Pieces of tissue stained in bulk may be infiltrated, imbedded, 

 and cut according to the ordinary methods. Under these circumstances, 

 section staining is not necessary unless a still further differentiation be 

 desired. 



In general, then, the treatment of the object is somewhat as fol- 

 lows : First, it is fixed in some one of the fixing fluids already described, 

 then carefully washed, and in certain cases stained in bulk before infiltrat- 

 ing with paraffin or celloidin ; or the staining may be postponed until 

 the tissue has been cut. In the latter case, the sections are subjected to 

 the stain either loose or fastened to the slide or cover-slip. 



In all cases it is absolutely essential that the paraffin be entirely 

 removed. After the sections have been stained and washed, they are 

 transferred to absolute alcohol in case it be desired to- mount them in 

 some resinous medium. They may also be mounted in glycerin or 

 acetate of potash, into which they may be passed directly from distilled 

 water. 



The method of staining tissues in sections or in bulk is shown in 

 the following diagrams : 



Absolute alcohol 



Wash in 

 water 



4- 



Alcohol 



s 



Absolute alcohol 



Wash in acid 

 alcohol 



4- 



Alcohol 



METHODS OF IMPREGNATION. 



The impregnation methods differ from the staining methods in that 

 in the latter the coloration is obtained by reagents in solution, while in 

 the former the tissues are filled with fine particles which enter into com- 

 bination with certain constituents of the tissue elements and are reduced 

 in them. 



Silver Nitrate Method. This method was suggested by Krause ; 

 it was, however, brought to prominence by v. Recklinghausen. It is 

 especially useful for staining the intercellular substances of epithelium, 

 endothelium, and mesothelium and the ground -substance of connective 



