PROCESS OF OSSIFICATION. 109 



same manner, except that the treatment with osmic 

 acid is here unnecessary. The preparations can be 

 mounted at once in glycerine. 



Preparation 10. To trace the later steps of the 

 ossification, it is requisite to obtain sections extending 

 rather more deeply into the newly-formed bone than is 

 possible whilst this still retains its earthy salts. For 

 this purpose, therefore, the hone, which may with advan- 

 tage be considerably smaller than that of the new-born 

 kitten one from a small foatus, for example is decalci- 

 fied in chromic or picric acid in the same way as was 

 employed for the deealcification of pieces of the fully- 

 developed bone (Preps. 4 and 5). But if the foetal bone 

 is small, the time necessary for such decalcification will 

 be very much shorter than was requisite for the dense 

 adult bone. Jn order to cut a longitudinal section suffi- 

 ciently extensive and thin, it will be necessary to embed 

 the bone in the wax mass (chap, x.), and the sections 

 obtained may be stained with logwood, or successively 

 with both logwood and carmine, and mounted in dammar 

 varnish in the way usually employed for treating sections. 

 A still better plan is to stain the bone entire with an 

 alcoholic solution of magenta, allow it to become per- 

 meated first with oil of cloves and then with melted 

 cacao-butter, and afterwards embed in cacao-butter, treat- 

 ing the sections with warm oil of cloves to dissolve out 

 the fat, and then mounting in dammar varnish. Or the 

 stained bone may be permeated with gurn, placed in spirit 

 containing one-sixth its volume of water to harden the 

 gum within the tissue, embedded in wax mass, cut, and 

 the sections placed in water to dissolve out the gum. 

 The .object of allowing a tissue of this nature, which con- 

 sists of hard and soft parts intermingled, to become 

 permeated by the substance above recommended, is that 

 the soft parts and cavities may be filled up by a hard 

 material, so that the tissue may offer a uniform resistance 

 to the razor and the parts of a section may cohere ; 

 otherwise the soft parts are very apt to become separated 

 from the hard. 



But since these processes are somewhat complicated, 

 the student is recommended to defer them for a while 

 10 



