2 "THE COMING OF MAN 



30,000,000 years to geologic time. The amount was considered 

 by him very conservative, and by most geologists as quite 

 inadequate.^ It is a minimum. The weight of evidence 

 seems to favor a length of from 90,000,000 to 120,000,000 

 years; some would make it much greater. 



Into this ancient world life stole very quietly and without 

 observation. Our most primitive forms of life, and they have 

 already advanced far, are the bacteria.^ They are exceedingly 

 minute, thousands together would not cover the comma on a 

 page of print. They seem to be composed of a substance 

 which we may call protoplasm. Many are too small to be 

 visible under the highest powers of our microscopes; and 

 we still know comparatively little of the finer structure of 

 even the higher and larger forms. 



They show great variety in size, form and structure. 

 Usually they resemble spheres or short rods; some approach 

 the lowest unicellular animals, the protozoa; others are scarcely 

 distinguishable from the lowest plants, the protophyta. They 

 form a group showing great variety, are exceedingly gener- 

 alized, and the persistent survival or development of such 

 a host of forms is the highest testimonial to the dour vitality 

 of the stock. 



Wherever life is possible there we find bacteria, in the 

 sea, in hot springs, in the frozen north, on mountain-rocks, 

 almost everywhere in the uppermost four or five feet of the 

 soil, in the bodies of plants and animals. They fit into every 

 crack and cranny in the world. Some flourish in light and 

 air, to others these are harmful or destructive. They ask 

 very little from nature, take whatever she offers and thrive."* 



They are admirably adapted to live in an inorganic world 

 or on dead material. Plants and animals die. Under the 

 influence of the bacteria the proteins of their bodies are 

 changed over into ammonia, and finally into nitrates, fit food 

 for plants; other compounds are similarly handled. They 



2 H. 85. 



2 2: 26. no. 



* G. 80. 



