50 THE INVISIBLE WORLD 



thing of life, the collective life of all the cells of 

 any one plant or animal is the whole life of that 

 plant or animal. And as the entire vegetable and 

 animal kingdoms are built up with these tiny bits 

 of protoplasm, it would be plainly possible, by 

 estimating at any time the approximate number of 

 cells on the earth, to determine thereby the ap- 

 proximate volume of life on the earth. 



But the object here in view is to think of the 

 cell, in all this volume of life, as a microbe. It 

 has so many properties similar to, if not identical 

 with, those of the microbe, that one seems com- 

 pelled to think of the cell as a being not only re- 

 sembling, but often the same as, the other being. 



The two beings in their primitive form consist 

 each of a tiny bit of protoplasm. In this respect 

 they certainly are alike, if not identical. 



By virtue of this the two beings have each the 

 power to seize hold of other kinds of matter, to 

 digest this matter and transform it into proto- 

 plasm, and thus to make it a part of themselves. 

 In this respect the two beings are identical. Each 

 is a manufacturer of protoplasm. 



The two beings are alike in the organs which, 

 sooner or later, appear in each. Each has, or may 

 have, the nucleus, the granules and the protective 

 membrane. 



The two beings are similar in respect to size. 

 Each is microscopical far too small to be seen 

 by the unaided eye. 



Cells, like microbes, vary in size. Some are so 



