THE CELL AND PROTOPLASM. 85 



together into groups to form colonies. Such colo- 

 nies are animals or plants. The cells divide the 

 work of the colony among themselves, each cell 

 adopting a form best adapted for the special work 

 it has to do. The animal or plant is thus simply 

 an aggregate of cells, and its activities are the 

 sum of the activities of its separate cells; just as 

 the activities of a city are the sum of the activities 

 of its individual inhabitants. The bit of proto- 

 plasm was the unit, and this was a chemical com- 

 pound or a simple mixture of compounds to whose 

 combined physical properties we have given the 

 name vitality. 



The Decline of the Reign of Protoplasm. Hard- 

 ly had this extreme chemical theory of life been 

 clearly conceived before accumulating facts began 

 to show that it is untenable and that it must at 

 least be vastly modified before it can be received. 

 The foundation of the chemical theory of life 

 was the conception that protoplasm is a definite 

 though complex chemical compound. But after a 

 few years' study it appeared that such a concep- 

 tion of protoplasm was incorrect. It had long 

 been suspected that protoplasm was more complex 

 than was at first thought. It was not even at the 

 outset found to be perfectly homogeneous, but 

 was seen to contain minute granules, together 

 with bodies of larger size. Although these bodies 

 were seen they were regarded as accidental or sec- 

 ondary, and were not thought of as forming any 

 serious objection to the conception of protoplasm 

 as a definite chemical compound. But modern 

 opticians improved their microscopes, and micro- 

 scopists greatly improved their methods. With 

 the new microscopes and new methods there be- 

 gan to appear, about twenty years ago, new reve- 



