Physiology 449 



when the medium supports growth of the bacteria, may be controlled by 

 using non-nutrient basal media (14, 42, 253, 258, 315). 



A wide variety of bacteria may serve as food for particular ciliates. 

 About 20 species, as individual suspensions in salt solutions, were each 

 adequate for growth of Tetrahymena pyriformis (253). Killed yeasts and 

 washed and killed suspensions of green flagellates also were satisfactory, 

 although living flagellates failed to support growth in serial transfers. On 

 the other hand, Perispira ovum thrives on living Eiiglena gracilis (93), 

 and Tetrahymejia pyriformis grows on either Chilomonas parainecium or 

 Polytoma oceUatum (182). For Colpidium colpoda, species of Entero- 

 bacteriaceae are more satisfactory than Bacillaceae (42). Killed bacteria 

 seem to be an inadequate diet for Colpoda duodenaria (548). Likewise, 

 Pleurotricha lanceolata and Stylonychia piistiilata can be grown on living 

 Tetrahymena geleii but not on killed ciliates (317). Just what heat-labile 

 factors, supplied by living organisms, are significant in such cases is still 

 unknown. However, Didinium nasutum is said to have lost the ability to 

 synthesize peptidases and must obtain these enzymes from the living 

 Paramecium which it ingests (101). 



Definitive observations on food requirements of ciliates awaited, first 

 of all, the establishment of pure cultures. This step was taken some 

 thirty years ago when A. Lwoff isolated Tetrahyrnerm (Glauco7na) pyri- 

 formis'' in a peptone medium. Comparative data on various culture media 

 were published later (340). These observations furnished a timely stimu- 

 lus, and within a relatively few years, additional bacteria-free strains — 

 referred to the genera Colpidium, Colpoda, Glaucoma, Tetrahymena, 

 Loxocephalus, and Paramecium — were isolated by other workers (274). 

 With a few exceptions, culture media included solutions of commercial 

 peptones, yeast-extract or yeast autolysates, usually supplemented with 

 inorganic salts. Such media as those of Glaser and Coria (160, 161, 162) 

 Avere more complex. Although Parameciinn bursaria has been maintained 

 in peptone media (322), cultivation of other species of Paramecium has 

 proven more difficult. However, P. aurelia (564) and P. multi-micronu- 

 cleatum (262) are now in pure culture and investigations on their food 

 requirements are in progress. 



The next progressive step led toward the development of chemically 

 defined culture media (349). The first apparently successful results were 

 those of Kline (298) with Colpidium striatum. Unfortunately, Kline's 

 strain of C. striatum seems to have been lost and several other strains 

 have failed to grow in his medium. 



Much better results have been obtained with somewhat similar media 



' This ciliate is a strain of Tetrahyinena gelii, a genus and species erected by Furga- 

 son (138) to include strains of "Colpidium campyhim," "C. striatutn," "Glaucoma pyri- 

 formis." Letter designations for various strains, such as T. geleii H and T. geleii W, 

 have since been proposed (72, 279). The name of the species apparently should be 

 Tetrahymena pyriformis (see Chapter VII). 



