102 PRACTICAL HISTOLOGY. 



transparent for any of the details of structure to be 

 made out. On the whole it is perhaps advisable to 

 purchase one or two good specimens rather than 

 devote a large amount of time to the manufacture 

 of what may after all turn out to be but an indif- 

 ferent preparation. Sections of bard bone and of 

 teeth are amongst the very few histological prepara- 

 tions which are usually better made by those who 

 make a business of preparing, microscopic specimens 

 for sale than by the student himself. 



Preparation 3. In addition to sections of hard 

 bone which are made by grinding in the manner 

 above described, a portion of a well-macerated bone 

 may be placed in a solution of hydrochloric acid 

 (10 parts of the commercial acid to 100 of water) 

 until all the earthy matter is dissolved ; the piece is 

 then steeped in a very weak solution of carbonate 

 of soda to free it from the remains of the acid, and 

 sections may then be made with a razor or sharp 

 scalpel and mounted in glycerine. But these decal- 

 cified specimens in no way illustrate the structure 

 of the tissue so well as the others. 



Preparation 4. It is, however, quite another 

 question with regard to bones which have not been 

 submitted to previous maceration. For it is to be 

 remembered that in considering the structure of a 

 bone we have to deal not merely with the bony 

 matter pure and simple and its included cavities, 

 but that there are in addition the soft contents of 

 those cavities the corpuscles in the lacunae, the 

 bloodvessels in the Haversian canals, and the marrow 

 in the medullary cavity and in the interspaces of the 

 spongy tissue. In order properly to view these 

 perishable structures, we must employ a reagent 

 which will at the same time decalcify and soften 

 the hard matter and preserve and harden the in- 

 cluded soft tissues. Such a reagent is to be found 

 in a solution of chromic acid, but ns the decalcify- 

 ing powers of this are but feeble, the portions of 

 bone placed in it must be as small as possible, and a 



