7 



THE STORY OF THE LIVING MACHINE. 



the distinction between formed material and 

 cell body is a convenient one and may well 

 be retained in the discussion 

 of cells. In our discussion of 

 the fundamental vital proper- 

 ties we are only concerned in 

 the cell substance, the formed 

 material having nothing to do 

 with fundamental activities of 

 life, although it forms largely 

 the secondary ma- 

 chinery which we 

 have already studied. 

 In all higher an- 



imals and plants the 

 FIG. 18. Connective rf r , r . . , , 



tissue. The cells hie of the individual 

 of the tissue are begins as a single 



vum r a sin s' e 



cell, and as it grows 

 the cells increase 

 rapidly until the adult is formed out of 

 hundreds of millions of cells. As these 

 cells become numerous they cease, after 

 a little, to be alike. They assume differ- 

 ent shapes which are adapted to the 

 different duties they are to perform. 

 Thus, those cells which are to form bone 

 soon become different from those which 

 are to form muscle, and those which are 

 to form the blood are quite unlike those A* piecT of 

 which are to produce the hairs. By nerve fibre, 

 means of such a differentiation there ceiTwftVits 

 arises a very complex mass of cells, nucieusat. 

 with great variety in shape and function. 



It should be noticed further that there are 

 some animals and plants in which the whole 



matter at/. 



FIG. 19. 



