36 



PROTOZOA 



upon the force of the stimulus, In some cases the reaction being 

 positive and in others negative. 



Economic Importance of Ciliates.^ — Bursaria is said to produce 

 an odor in water supplies similar to that of a salt marsh. Vorticella 

 and Stentor (Fig. 14, A) are frequently found in "'pipe moss " and 

 along edges of reservoirs and dams, but are not injurious. Ciliates 

 clean up bacteria in sewage disposal plants. 



Fig 



^r Nucleus 



ff~^ ^^//e/ 



Controcfile i/ocuo/e 



Stentor sp. (After Stein. Drawn 

 by H. N. Lammers.) 



Fig. i^B. Opalina. (After 

 Biitschli. Drawn by H. N. 

 Lammers.) 



Parasitic Ciliates. — Balantidium coli and Balantidium minutum 

 have been found in the intestines of human beings infected with 



® In considering the value of Protozoa, we must remember that they are mar- 

 velously adapted to laboratory experimentation. Calkins, Woodruff, Jennings, and 

 others have demonstrated this by a variety of fundamental studies on life processes. 

 Packard has studied the influence of salts on the division rate of Paramecium, adding to 

 our information facts which may have significance in efforts at the control of cancer. 

 (Packard, C. 1926. Effect of sodium on the rate of cell division. Jour, of Cancer 

 Research, vol. 10, pages 1-14.) 



