RELATIONS OF PROTOZOA TO MAN 



75 



Uroglenops'is Dinobryon Synura 



Figure 39. Colonial flagellates that may render water unfit to drink. Highly magnified. 



bry'on is more like that of rockweed. Cera- 

 tium produces a vile stench. ChlamydomO' 

 nas and Mallomonas are less objectionable 

 as their odors have an aromatic quality. 

 Waters which harbor Cryptomonas may 

 even smell like "candied violets." 



All these odors are due to aromatic oils 

 which are produced by the organisms during 

 growth and liberated when they die and 

 undergo decomposition. Treatment of the 

 water supply with copper sulfate is stand- 

 ard procedure for the control of these bad- 

 smelling protozoans. 



Some species of aquatic Protozoa, on the 

 other hand, are really beneficial to man. 

 Kudo (1947) states that since protozoans 

 feed extensively on bacteria, they prevent 

 the bacteria from reaching the saturation 

 point, that is, from becoming so numerous 

 that they cease to multiply and thus no 

 longer perform the important function of 

 destroying waste materials which continu- 

 ally pollute the waters. Protozoa therefore 

 help indirectly in the purification of water. 



In many aquatic situations. Protozoa serve 

 as food for small insects, crustaceans, and 

 the like; these organisms, in turn, are fed on 

 extensively by many species of fish. Of 

 course, other protozoans live as parasites of 



fish. The Mj'xosporidia, especially, cause the 

 death of large numbers of commercially 

 important species. The relations of the Pro- 

 tozoa to aquatic biology are therefore many 

 and varied. 



SOIL PROTOZOA 



Soil fertility is affected not only by bac- 

 terial action, but also by the protozoan 

 fauna which may be present. It has long 

 been held that the Protozoa probably reduce 

 the numbers of nitrogen-fixing bacteria and 

 thus limit the production of nitrates so es- 

 sential for soil fertility. Between 200 and 

 300 species have been identified from soils, 

 the small flagellates being the most com- 

 mon. Amoeboid types and ciliatcs follow in 

 the order named. Most soil-inhabiting Pro- 

 tozoa are found near the surface, the great- 

 est concentration being at a depth of about 

 Ys inch, and few are found at depths of 12 

 to 18 inches. Very few are ever found in 

 subsoil. Certain well-adapted species show 

 a surprising geographical distribution. 

 Amoeba proteus, for example, has been 

 found in soils from almost every part of 

 the world. Trinema is represented in soils 



