CHAPTER VIII 



THE TECHNIQUE AND SIGNIFICANCE OF CONTROL 

 IN PROTOZOAN CULTURE 



George W. Kidder 



Introduction 

 During the last few years there has come to be an appreciation of 

 methods of culturing Protozoa which will permit the investigator to 

 determine the conditions under which his study is being made. Studies 

 of populations and the various interesting and important factors in- 

 volved, mass physiology, nutrition, and numerous other phases of cellu- 

 lar activity may be profitably dealt with by the student of the Protozoa 

 only when he can be sure that the effects noted are due to the conditions 

 under investigation. The science of protozoology has passed through the 

 phase of "pure-mixed" methods of culture. This term simply means 

 that a single strain of Protozoa is grown in association with a chance 

 combination of other microorganisms, usually bacteria. Many valuable 

 and thought-provoking contributions, based upon this method, have 

 been made, and these contributions have paved the way to the more pre- 

 cise evaluations of the present. 



In the culture of practically any species of Protozoa, it may be safely 

 said that the bacteria as a group offer the most serious obstacle to con- 

 trolled conditions. Experimental modifications of factors such as nutritive 

 materials, temperature, oxygen or carbon dioxide tensions, oxydation- 

 reduction potentials, and so forth, may produce effects, but whether these 

 effects are the result of changes in protozoan activity per se, or are sec- 

 ondary through the change of activity of the bacteria, is usually nearly 

 or totally obscure. These facts are recognized, and there has been built 

 up a body of literature reporting progress in methods which will allow 

 for the control or, better still, the elimination of bacteria. Numerous in- 

 vestigators have succeeded in sterilizing various species of Protozoa and 

 have made great strides in advancing our knowledge of cellular activities 

 through the use of pure cultures. 



