74 THE STORY OF LIFE'S MECHANISM. 



most ingenious speculation, he could never under- 

 stand the real significance of the cities, since he 

 is not acquainted with the actual living unit. 

 Imagine now, if you will, that this supramundane 

 observer invents a telescope which enables him 

 to perceive more minute objects and thus dis- 

 covers human beings. What a complete revolu- 

 tion this would make in his knowledge of mun- 

 dane affairs ! We can imagine how rapidly dis- 

 covery would follow discovery ; how it would be 

 found that it was the human beings that build the 

 houses, construct and run the railroads, and con- 

 trol the growth of the cities according to their 

 fancy ; and, lastly, how it would be learned that 

 it is the human being alone that grows and 

 multiplies and that all else is the result of 

 his activities. Such a supramundane observer 

 would find himself entering into a new era, in 

 which all his previous knowledge would sink 

 into oblivion. 



Something of this same sort of revolution was 

 inaugurated in the study of living things by the 

 discovery of cells and protoplasms. Animals and 

 plants had been studied for centuries and many 

 accurate and painstaking observations had been 

 made upon them. Monumental masses of evi- 

 dence had been collected bearing upon their 

 shapes, sizes, distribution, and relations. Anato- 

 my had long occupied the attention of naturalists, 

 and the general structure of animals and plants 

 was already well known. But the discoveries 

 starting in the fourth decade of the century by 

 disclosing the unity of activity changed the 

 aspect of biological science. 



