CONTROL OF CULTURES 469 



organism. This is easily accomplished in a number of cases, even to the 

 establishment in media containing only dissolved proteins. A large num- 

 ber of flagellates probably exist in nature by the utilization of dissolved 

 substances and, when sterilized, continue to employ this type of nutri- 

 tion. Among the free-living ciliates, all species are known to possess oral 

 openings into which solid foods are drawn. Some of these, however, are 

 able to live on dissolved proteins in pure culture, e.g., Tetrahymena. 

 Other types may be able to obtain only a small amount of nutriment 

 from the dissolved proteins, but are able to feed on nonliving particu- 

 late matter. This was found to be the case in this laboratory with Glau- 

 cojna sc'mtillans (unpublished work). When sterilized ciliates were 

 placed in a wide variety of media containing dissolved proteins, very 

 little multiplication took place. However, good growth resulted in un- 

 filtered Yeast Harris, containing quantities of broken-down yeast cells. 

 Still other types of free-living ciliates appear to be unable to exist with- 

 out living organisms as food. This may be the case with the true carni- 

 vores, and here there is an excellent opportunity to make some interesting 

 studies on the "Zweigliedrige Kulture" without employing bacteria. It 

 is only necessary to be able to grow the food Protozoa in pure culture 

 and to supply it to the sterile carnivores. Some work along these lines 

 has already been started in our laboratory, using pure cultures of Tetra- 

 hymena as the food organism and studying the effects of such a diet on 

 G. vorax (Kidder, Lilly, and Claff, 1940). Similar cultures of Stylony- 

 chia pustulata are being studied by D. M. Lilly (Lilly, 1940), and the 

 nutritional requirements of a E//glena- feeding Peris p'na is being investi- 

 gated by the author and V. C. Dewey in this laboratory. Oehler (1919) 

 stated that Colpoda steinii was unable to live on dissolved nutrients but 

 would live on particulate matter, including dead bacteria. Kidder and 

 Stuart (1939) ^ete unable to confirm Oehler's results, but found that 

 C. steinii was dependent upon living organisms. They remark, however, 

 that the possibility does exist that some combination of food substances 

 and conditions, as yet not known, may possibly allow this important 

 ciliate to reproduce in the absence of living organisms. 



It may be inferred from what has already been said that the estab- 

 lishment of a sterile protozoan in culture is not a routine matter. Of 

 course the goal is a pure culture, for more precise control is then possible. 

 With some types it has been found that growth follows when they are 



