MODERN METHODS OF EXAMINATION. 63 



tion may be cut by such an instrument after inserting 

 the structure desired in a piece of carrot, etc., which may 

 be placed in the tube ; or the tube may be filled with wax, 

 etc., and the specimen imbedded. Bones, teeth, shells, 

 corals, minerals, etc., require to be cut with fine saws, or 

 a disk of thin iron on a lapidary's wheel, and filed or 

 ground down to the requisite thinness, then polished with 

 emery, rouge, etc. The green oxide of chromium has 

 been suggested to me as a useful polishing powder for 

 hard substances. For calcareous substances, files and 

 hones will suffice to reduce the thickness, and putty 



FIG. 34. 



Section-Cutter. 



powder or jewellers' rouge for polishing. They should 

 be mounted in Canada balsam. 



Staining Tissues. Certain elements, not previously visi- 

 ble, can often be made evident by certain coloring matters, 

 by which some constituents become more quickly or more 

 thoroughly stained than others. The " germinal matter," 

 or " bioplasm " of Dr. Beale, identical with the " proto- 

 plasm " or " sarcode " of other observers, may thus be dis- 

 tinguished from the " formed materials " or " tissue ele- 



