THE PROTOZOA 231 



water contained an average of 112,000,000 protozoan individ- 

 uals (Kofoid). 



The numbers of Protozoa in different kinds of water are in- 

 dicated by the following statistics (Whipple). 



A flowing brook contained 10 per cubic centimeter. 



A reservoir contained 97 per cubic centimeter. 



A pond contained 666 per cubic centimeter. 



The trouble caused by the Protozoa is chiefly due to their odor 

 and taste. Besides this, Protozoa may cause temporary intes- 

 tinal disorders in people not accustomed to a certain kind of 

 water. On the other hand, some Protozoa undoubtedly aid in 

 purifying water of Bacteria; for example, the flagellate Bodo 

 greatly reduces the number of typhoid fever germs by using 

 them for food. 



Some of the common species of Protozoa that cause trouble are 

 Urogtena (Fig. 137, A), which has a fishy or oily odor ; Synura, 

 with an odor of ripe cucumbers and a bitter and spicy taste; and 

 Bursaria, with an odor resembling that of a salt marsh. 



The water in reservoirs may be purified by the use of copper 

 sulphate (blue vitriol). About one part of copper sulphate to 

 from five to twenty million parts of water should be used. This 

 should be placed in a bag and dragged through the water behind 

 a boat until all is dissolved and thoroughly distributed. Copper 

 sulphate is poisonous, but the amount used is so small as to be 

 harmless. 



Colonial Protozoa. Protozoa are said to be one-celled ani- 

 mals, but many species live more or less firmly fastened together 

 in groups or colonies. In some cases the members of the colony 

 are rather loosely united, as in Carchesium, a near relative of 

 Vorticella, which occurs in groups fastened together by thin 

 stalks. Other species may consist of many members embedded 

 in a gelatinous matrix, such as Uroglena (Fig. 137, A), a relative 

 of Euglena. 



VOL vox. In one species, Volwx globator (Fig. 137, B), the 

 members of the colony are connected with one another by strands 



