Phylum I 



Protozoa, Class Mastigophora 



GROWTH OF FREE-LIVING PROTOZOA 

 IN PURE CULTURES 



R. P. Hall, University College, New York University 



INTRODUCTION 



THE pure-culture technique offers certain definite advantages in the 

 maintenance of free-living Protozoa in the laboratory. As a depend- 

 able source of material for class use, bacteria-free cultures far surpass in 

 value the usual hay infusions. Thus, a number of species of flagellates 

 and ciliates have been maintained in our laboratory over periods ranging 

 from two to six years, with an abundant supply of each type always avail- 

 able. In a suitable medium, bacteria-free cultures remain viable for 

 several months; hence frequent transfers are unnecessary for the 

 maintenance of stock cultures. The technique is simple and requires rela- 

 tively little equipment and no more than a rudimentary knowledge of 

 bacteriological procedures. Bacteria-free cultures are even more valu- 

 able as a source of material for experimental studies. In physiological 

 investigations the advantages of the elimination of bacteria in the precise 

 control of experimental conditions are obvious. Biochemical investiga- 

 tions, impossible a few years ago, may now be carried out on free- 

 living Protozoa with almost the same facility as in the case of bacteria. 

 In short, the establishment of bacteria-free cultures opens to the pro- 

 tozoologist, physiologist, and biochemist a wide field of investigation 

 which promises to add much to our knowledge of the morphology, life 

 history, and metabolism of Protozoa. 



Two general methods have been followed in the growth of Protozoa in 

 the absence of other living micro-organisms. In the first, the organisms 

 have been washed free of bacteria and grown in sterile peptone solutions 

 or similar media. In the other method, used particularly for ciliates, 

 the Protozoa have first been freed from bacteria and then placed in 

 suspensions of killed bacteria or other micro-organisms. Ciliates and 

 other Protozoa have also been grown by various workers on single strains 

 of living bacteria, yeasts, algae, and small Protozoa. 



