32 AGRICULTURAL BACTERIOLOGY 



the result of the profuseness with which they are produced 

 and the ease with which they are distributed. 



Protozoa. This term is applied to unicellular animals, 

 some of which are of interest to us because of their relation 

 to bacteria, and because some of them produce diseases in 

 man and in domestic animals in much the same way as do 

 the bacteria. 



The animal cell wall lacks the rigidity and firmness of 

 the plant cell wall. For this reason, the protozoa do not 

 have the definiteness of form that marks the unicellular bac- 

 teria and yeasts. 



Many of the protozoa ingest solid food, again a differentia- 

 tion from the unicellular plants. Bacteria serve as food for 

 some of the protozoa to be found in soil and water. 



