72 NORMAL HISTOLOGY. 



them possess very nearly the same refractive power as 

 the basement substance. The cell-spaces and canaliculi 

 are best studied in thin sections of hard bone, which 

 have been macerated for some time, so as to remove the 

 medullary fat and other soft parts, and then dried. 

 Transverse or longitudinal sections may be made, the 

 latter being most easily prepared, because sections in 

 this direction are less brittle. 



A small piece, as thin as possible, should be sawn from 

 the bone (the diaphysis of a human long bone answers 

 very well) in the proper direction ; this is ground down 

 very thin on a whetstone or grindstone, or on a plate of 

 glass with emery powder, the section being held down 

 with the ball of the finger or a bit of soft cork. When 

 it has become quite thin, so as to be almost transparent, 

 it is polished on a dry oil-stone free from grease, and 

 then carefully washed and brushed under water with a 

 fine pencil to remove particles of dirt. It is now allowed 

 to dry, and is mounted in balsam. For this purpose the 

 semi-fluid Canada balsam, such as is used for ordinary 

 mounting, should not be employed, because it would 

 run into the lacunae and canaliculi, and render them 

 invisible. A bit of quite hard and solid balsam should 

 be placed on a slide and heated until it melts ; just as it 

 begins to fairly cool, but before it gets at all hard, the 

 slip of bone is quickly immersed in the drop and covered. 

 If the proper moment has been chosen, when the balsam 

 is neither too hot nor too cold, the lacunae and canali- 

 culi are clearly defined by reason of the air with which 

 they are filled. Usually, however, in the most successful 

 preparations, in the very thin parts or at the edges, part 



