Ophryoglenidae 105 



Pringsheim (1915) grew Paramecium bursaria with its green commensals 

 in an inorganic medium similar to Knop. 



In addition, Paramecium caudatum may be grown in an enormously 

 complex medium developed by Glaser and Coria (1935). The writer 

 (unpublished work) verified these results using both rabbit and monkey 

 kidney ; here again growth is not as vigorous as in the presence of living 

 bacteria. Failure, reported previously (Hetherington, 1934c), was due 

 to the use of a Seitz bacteriological filter rather than a Berkefeld. The 

 filter pads, not the metal of the Seitz filter, contribute a toxic substance 

 to the filtrate. 



While it may stretch the definition of pure culture somewhat to include 

 a medium which contains fresh rabbit kidney, these investigations are 

 illuminating, as will be indicated in the next following section. 



CULTURE ON SINGLE STRAINS OF BACTERIA 



Freshwater ciliates capture and ingest their food, as higher animals 

 do. There is no evidence that they can obtain energy or build proto- 

 plasm from simpler nutrients than required by higher organisms. 



A division rate of 8.28 may be maintained in the case of Glaucoma 

 scintillans on living bacteria in non-nutrient salt solution (25 C). A 

 small quantity of Bacillus megatherium, strain D 20 of the Stanford 

 University Bacteriology Department Collection, having a diameter of 

 about 1 mm., is removed from a 24-hour nutrient plate by means of a 

 platinum needle, put in 0.5 cc. of Peters' medium, together with one 

 Glaucoma. Transfer is made every 24 hours. No difference can be 

 observed between washed and unwashed bacteria. 



Turning to larger ciliates, Colpidium colpoda (nop) grows with a 

 division rate of 4.33 (24 C.) on Aerobacter aerogenes, strain A 2 Stan- 

 ford Collection, in the following medium (Hetherington, 1934b) : 



Peptone, Dif co o.i % 



Dextrose, Baker's C. P. powd 0.1% 



This is made up in Peters' medium, and autoclaved at 15 lbs. pressure for 

 15 minutes. 



Colpidium campylum (50-90/*) has similar nutritive requirements, 

 but is more resistant, and will grow faster in a 0.35% concentration of 

 nutrient. Like Colpidium colpoda, it has never been grown in pure 

 culture. 



Paramecium caudatum and P. aurelia grow luxuriantly in the same 

 system (Aer. aerogenes -f- 0.2% peptone-dextrose), either in tiny isola- 

 tion volumes or in flasks. This is a more constant medium than the 

 Pseudomonas otio/w-powdered lettuce medium reported by Giese and 

 Taylor (1935), which is a technique apparently borrowed from the ex- 



