INTRODUCTION 11 



Sanitary betterment and improvement are fundamental re- 

 quirements in the modern civilized world. One of man's neces- 

 sities is safe drinking water. The majority of Protozoa live in 

 water and many of them seem to be responsible, if present in 

 sufficiently large numbers, for giving certain colors or odors to 

 the waters of reservoirs or ponds. For example, according to 

 Whipple, the chrysomonad Synura, which produces an oily 

 substance as a result of metabolic activities, was found to be 

 the cause of "cucumber" odor in several water supplies, and 

 Calkins found that the oil droplets which were developed in 

 a large number of individuals of Uroglenopsis americana be- 

 came the cause of an offensive odor of the water in which they 

 lived. Bursaria, Ceratium, Dinobryon, Mallomonas, etc., if 

 present in large numbers, may give a "fishy" odor. 



But these Protozoa which are occasionally harmful are com- 

 paratively small in number compared with those which are bene- 

 ficial to man. It is generally understood that bacteria feed on 

 various waste materials present in polluted water, but that upon 

 reaching a certain concentration, they would cease multiplying 

 and would allow the excess organic substances to undergo de- 

 composition. Numerous holozoic Protozoa, however, feed upon 

 the bacteria and prevent them from reaching the saturation 

 population. Protozoa thus help indirectly in the purification of 

 the water. Protozoology therefore must be considered as an 

 important part of modern sanitary science. 



Young fish feed extensively on small aquatic organisms such 

 as larvae of insects, small crustaceans, annelids, etc., all of which 

 depend largely upon Protozoa and Protophyta as sources of 

 food supply. Thus the fish are indirectly dependent upon Pro- 

 tozoa as food material. On the other hand there are numbers of 

 Protozoa which prey upon fish. The Myxosporidia are almost 

 exclusively parasites of fish and often cause death to large 

 numbers of commercially important fish. Success in fish-cul- 

 ture, therefore, requires among other things a good knowledge 

 of Protozoa. 



Since Russel and Hutchinson suggested some twenty years 

 ago that Protozoa are probably a cause of limitation of the 

 numbers, and therefore the activities, of bacteria in the soil and 

 thus tend to decrease the amount of nitrogen which is given to 



