1894.J MICROSCOPICAL JOURNAL. 213 



To EXAMINE THE OSEOUS LAYERS. — It is possible to 



study these in the preceding preparations, yet we recom- 

 mend another process. Dehydrate a section in absolute 

 alcohol. Replace the latter by a drop of oil of bergamot, 

 [clove, cajeput*, or other essential oil] and when trans- 

 parent mount in balsam. Here the osteoblasts and the 

 canaliculi, filled with the resin, are hardly visible, but 

 the arrangement of the lamellae is very evident. 



SECTIONS OF FRESH BONE. 



A small fragment of the femur as fresh as possible is 

 put in alcohol for a few hours, thence transferred to at 

 least a litre of a saturated solution of picric acid, to which 

 is added 2 percent of nitric acid. Renew this liquid the 

 next day. If the piece is very small (a condition indis- 

 pensable to success), decalcification will be complete in 

 from 3 to 4 hours. This will be when the bone is flex- 

 ible and easily cut. Wash in a large quantity of water,' 

 which should be renewed until all acid is removed. 

 Harden by alcohol ; imbed in gum. Sections (made in 

 different directions through the bone) are washed until 

 the yellow color disappears, stained in picro-carmine, 

 and mounted in carbolic acid water or in glycerine. This 

 method is admirable for the study of ossification. 



To study the part taken by the vessels in the forma- 

 tion of bone, inject the arteries of a kitten with the Prus- 

 sian blue gelatine and put a femur for a week in 2 per 

 cent ammonia bichromate. Decalcify in an aqueous so- 

 lution of picric acid. Wash thoroughly, harden in alco- 

 hol, embed in gum, cut longitudinal sections and mount 

 in balsam. 



( To be continued.) 



Cementing on Glass. To cement brass or any other metal 

 upon glass, take one part caustic soda, 3 parts resin, 5 parts 

 water, and rub up well with plaster of Paris equal in weight to 

 half that of the above mixture. 



