Ophryoglenidae 103 



lines of Didinium is the result of feeding the Didinia on underfed Para- 

 mecia from an old, declining culture. All attempts to maintain cultures 

 of Didinium on starved, emaciated Paramecia have led without exception 

 in my experience to excessive conjugation, loss of the ability to encyst, 

 reduced division rate, structural abnormalities, and death of the Didinia 

 within two or three weeks at most. 



References 



For the culture of Didinium see also p. 63. 

 Family Chilodontidae 



For the culture of Chilodon see pp. 55 and 62. 

 For the culture of Chilodon cucullulus see p. 104. 



Family ophryoglenidae 



CONTROLLED CULTURES OF FRESHWATER CILIATES 



Alford Hetherlngton, Stanford University 



THE original mass-cultures which provide a varied abundance of 

 ciliates for observation and description prove unsatisfactory for the 

 needs of modern experimentation. Control of culture media has pro- 

 ceeded along two lines, the traditional objective of pure culture (i.e., cul- 

 ture in the absence of other life), and culture on a controlled source of 

 living food. Pure culture is so far successful only for some of the smaller 

 ciliates. 



At first sight, culture of the larger ciliates such as Stentor coeruleus or 

 Bursaria truncatella on pure cultures of, for instance, the small ciliate 

 Glaucoma pyriformis, would seem to promise a peculiarly elegant con- 

 trol of these animals which are so easily manipulated with the unaided 

 eye. For very perfect control the food animal could be washed before in- 

 troduction in known amounts into a simple inorganic medium containing 

 them. 



However it turned out that the conditions of survival of the larger 

 free-livi-ng ciliates are much more complex than was anticipated, an out- 

 come regretted by those who wish to use them simply as material for 

 physiological investigations, but of interest to those who are concerned 

 with the biology of micro-organisms as such. 



PURE CULTURE 



Sterilization of Ciliates. A method combining the advantages of mi- 

 gration and of washing was described by Hetherington (1934a). The 

 practice of bacteriological methods is assumed in that which follows. 



