4 "fHE COMING OF MAN 



stage of life chemistry. These bacteria derive both their 

 energy and their nutrition directly from inorganic chemical 

 compounds; such types were thus capable of living and 

 flourishing in the lifeless earth before the advent of continu- 

 ous sunshine and long before the first chlorophyllic stage 

 (algse) of the evolution of plant-life." They are anything 

 but structureless, but we still know very Iktle concerning their 

 structure. They are far from homogeneous. We find granules 

 of different shapes, sizes, and behavior toward stains; net- 

 works and strands of various character. Vacuoles play an 

 important part. We will return to this subject in our glance 

 at protozoa. 



The bacteria may have remained for ages the highest forms 

 of life. They cover a wide range of structure, complexity and 

 development. They laid the first and lowest yet discovered 

 tiers in the foundations of life. They still form an essential 

 link in its maintenance. They have done their part well and 

 thoroughly. Nature could afford to spend milHons of years 

 in their development. From them lines of inconceivable pos- 

 sibilities radiate. 



The Protozoa. Here again we find great variety, a host of 

 forms showing a long development, great adaptability and 

 wide distribution. We select for our example the amoeba, an 

 exceedingly common form which has attracted and held the 

 interest of all observers since its. first discovery. Though 

 far larger than the average bacterium, the amoeba is still 

 minute — from %oo to Yooo of an inch in diameter. It is 

 a single cell, consisting of nucleus and cytoplasm, two quite 

 distinct portions developed and differentiated out af the proto- 

 plasm of some ancient and far simpler and primitive bacterium. 

 The nucleus is a small body, staining deeply and showing the 

 presence of a very peculiar substance, chromatin. This sub- 

 stance is apparently present in many bacteria in small granules, 

 "a diffused nucleus"; in others it seems to be almost equally, 

 distributed through the protoplasm. 



The cytoplasm of the amoeba is a translucent, granular 



