THE STORY OF LIFES MECHANISM. 



'4 



FIG. 16. Frog's blood : a and 6 are the 

 cells; c is the liquid. 



material has been hardened by calcium phos- 

 phate, which gives the rigid consistency to the 

 r=?=r-_ bone. In some 



^'.vv; ::-_---- ;-.-.-_ _ animal tissues the 



formed material 

 is still greater in 

 amount. At Fig. 

 18, for example, 

 is a bit of con- 

 nective tissue, 

 made up of a 

 mass of fine 

 fibres which have 

 no resemblance 

 to cells, and indeed are not cells. These fibres 

 have, however, been made by cells, and a care- 

 ful study of such tissue 

 at proper places will show 

 the cells within it. The 

 cells shown in Fig. 18 

 (c) have secreted the fib- 

 rous material. Fig. 19 

 shows a cell composing 

 a bit of nerve. At Fig. 

 20 is a bit of muscle ; 

 the only trace of cellular 

 structure that it shows 

 is in the nuclei (n), but 

 if the muscle be studied FIG. n.-A bit of bone, showing 

 in a young condition its the cells embedded in the 



I -i . bony matter. 



cellular structure is more 



evident. Thus it happens in adult animals that 

 the cells which are large and clear at first, be- 

 come less and less evident, until the adult tissue 



