68 THE STORY OF THE LIVING MACHINE. 



3 

 3 



colour. The liquid may here again be regarded 

 as material produced by cells. At Fig. 17 is a 



bit of bone showing 

 small irregular cells 

 imbedded within a 

 large mass of mate- 

 rial which has been 

 deposited by the cell. 

 In this case the 

 formed material has 

 been hardened by 

 calcium phosphate, 

 which gives the rigid 

 consistency to the 

 bone. In some ani- 

 mal tissues the 

 formed material is 





FIG. 14. Various shaped wood cells 

 from plant tissue. 



still greater in 

 amount. At Fig. 18, 

 for example, is a bit 



of connective tissue, made up of a mass of fine 



fibres which have no resemblance to cells, and in- 



deedarenot cells. These fibres have,however,been 



made by cells, and a careful 



study of such tissue at proper 



places will show the cells with- 

 in it. The cells shown in 



Fig. 18 (t) have secreted the 



fibrous 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 (), but 



if the muscle be studied in a 



young condition its cellular FIG. 15. A bit of cartilage. 



