716 



THE MICROSCOPE. 



them approaches to a transverse one : for when the cells 

 are cut through their shorter 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 con- 

 densed light, the bone-cells and canaliculi will appear quite 

 white, and the intercellular substance, which was trans- 

 parent when viewed by transmitted light, is now perfectly 

 dark. The soft part consists 

 of the periosteum, which in- 

 vest the outer, and of the 

 medullary membrane, which 

 invests the inner surface, lines 

 the Haversian 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 



Fig. 349. A horizontal section of the short time in a dilute solution 



ZSk'SS&S .""&. of caustic potash. The animal 



bone-cells arrangedin parallel lines, matter mav be procured bv 

 There are no Haversian canals pre- . i .* ' i ITT * 

 sent ; and when this specimen is USing dilute hydrochloric acid 

 contrasted with that of fig. 347, inafpa/j n f nanafin nr>fn>i 

 it will be noticed that the canali- in SteaO. C caustic potasn _, 



cuii given off from each of the when all the earthy matter 



bone-cells of this fish are very few i 1-1 -11 



in number in comparison with 1S removed the Section Will 



that of the reptile. exhibit nearly the same form 



as when the earthy constituent was present ; and if then 

 viewed microscopically, it will be noticed that all the 

 parts characterising the section previous to its maceration 

 in the acid will be still visible, but not so distinct as 

 when both constitutents were in combination. When, 

 however, the animal matter is removed, the bone will not 

 exhibit the cells and the canaliculi, but is opaque and 

 very brittle, and nothing but the Haversian canals and a 



