PROCURING OBJECTS. 



97 



made of watch-spring. They should then be cemented on a 

 piece of glass ; filed to the proper thinness ; ground upon a 

 hone } and polished by a leather strap or piece of cloth charged 

 with putty powder (oxide of tin and lead), or carbonate of iron 

 (rouge). They may be mounted dry or in balsam. Both 

 transverse and longitudinal sections should be made. 



The sections may be cleaned from grease by soaking in sul- 

 phuric ether. 



The bloodvessels of bone when injected are rendered more 

 conspicuous if the earthy parts of the bone are removed by 

 means of an acid. They may then be kept in oil of turpentine, 

 which renders the tissue more transparent. 



Fig. 29. 



When animal tissues are consolidated by the deposition of 

 earthy matter within their cells and fibres, a hard, solid sub- 

 stance is produced. Sometimes the earthy matter crystallizes, 

 as in the teeth at other times it combines chemically with 

 the gelatine of the cells, as in bone. This deposition in bone 



9 



