BONE. 381 



into the Haversian canals ; whilst the canaliculi of the opposite side 

 communicate with those of the layer of canaliculi more external to 

 them ; and those in the outer row have most of their canaliculi given 

 off from that side of the bone-cell which is nearest its own Haversian 

 canal : hence arises the transparent white line which often may be 

 noticed as surrounding each concentric system of laminae and bone- 

 cells : in some cases, however, part of the bone-cells of the external 

 row anastomose with another series of bone-cells, which are situated 

 between the concentric laminae. The average length of the lacunae, or 

 bone-cells, in the human subject is the l-2000th of an inch ; they are of 

 an oval figure, and somewhat flattened on their opposite surfaces, and 

 are usually about one-third greater in thickness than they are in 

 breadth ; hence, as will be presently shown, it will become necessary to 

 know in what direction a specimen is cut, in order to judge of their 

 comparative size. The older anatomists supposed them, from their 

 opacity, to be little solid masses of bone ; but if the section be treated 

 with spirits of turpentine coloured with alkanet-root, or if it have been 

 soaked in very liquid Canada balsam for any great length of time, it 

 can then be unequivocally demonstrated that both these substances will 

 gain entrance into the bone-cells through the canaliculi. The bone- 

 cells, when viewed by transmitted light, for the most part appear per- 

 fectly opaque ; and they will appear the more opaque the nearer the 

 section of them approaches to a transverse one : for when the cells are 

 cut through their short diameter, they are often of such a depth that 

 the rays of light interfere with each other in their passage through 

 them, and darkness results ; whereas, if the section be made in the long 

 diameter of the cells, they will appear transparent. When viewed as 

 an opaque object, with a dark ground at the back and condensed light, 

 the bone-cells and canaliculi will appear quite white ; and the intercel- 

 lular substance, which was transparent when viewed by transmitted 

 light, is now perfectly dark. 



Thus much may be said to compose the hard part of the bone; we 

 must now turn our attention to the soft part. This, as has been before 

 stated, consists of the periosteum, which invests the outer, and of the 

 medullary membrane, which invests the inner surface, lines the Ha- 

 versian canals, and is continued from them, through the canaliculi, 

 into the interior of the bone-cells ; and of the cartilaginous or other 

 matrix, which forms the investment of the minute ossific granules. The 

 earthy matter of the bone may be readily shown by macerating the 

 section for a short time in a dilute solution of caustic potash. 



The animal matter may be procured by using dilute hydrochloric 



