38 



THE MICROBE AND ITS ACTIVITIES 



into organic or insoluble forms. Figs. 26 and 27 show two of 

 the most common types of soil algae. Fig. 28 shows a soil 

 diatom. 



The Protozoa of the Soil. — The protozoa are the most 

 elementary forms of life belonging to the animal kingdom. They 

 are all microscopic, unicellular, larger than bacteria and more 

 complex in their activities. They move either by means of cilia, 

 flagella, or pseudopodia. The nature of their locomotion is used 

 as a basis for their classification. They may be conveniently 

 grouped as follows: (1) The Ciliata, which include the ciliates 

 or infusoria; (2) the Mastigophora, which include the flagel- 



Fifi. 27. — Soil alga, Chlamydomonns 

 communis (from Bristol). 



Fir:. 28. — Soil diatom, Navicula 

 terricola (from Bristol). 



lates; and (3) the Rhizopoda, which include the amoebae. They 

 vary from naked forms to those which produce chitinous or 

 siliceous envelopes. All three groups are abundantly represented 

 in the soil, the smaller flagellates and amoebae being especially 

 abundant. Representatives of the various groups of protozoa 

 are shown in Figs. 29-33. 



Physiologically the protozoa vary considerably. Due to the 

 fact that it is very difficult to free protozoa from bacteria, the 

 exact nature of the physiology of these infinitesimal animals is 

 still a matter of dispute. Some of them at least are capable of 

 utilizing dead organic and inorganic substances from solution 

 and from solid particles. Many forms are capable of ingesting 



