68 



THE SCIENCE OF LIFE. 



d. In bone and other hard tissues, as the teeth, the 

 intercellular substance is solidified by salts of lime de- 

 posited in a modified form by molecular coalescence. 

 Sec. 3. In this case the bioplasm, or cell, is limited to 

 certain spaces, or lacuna, and receives nourishment 

 through small canals, or canaliculi. (Fig. 23.) 



FIG. 23. Transverse section of a long bone. a. Haversian canal, b. Concentric 

 laminae, c. Laminae of connection, d. Lacunae, with their system of tubes. 



e. Some fibrous structures may be formed by moving 

 particles of bioplasm, leaving behind them a thread of 

 formed material. In voluntary muscular fiber this formed 

 material is duplex, and in certain nerve-ganglia the fiber 



