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Scientific Proceedings (132) 



sistently positive until after the 24th observation. At the 25th 

 hour the first spores were observed in stained preparations. At 

 all times the majority of the growth could be centrifuged to the 

 bottom of the tube, showing that the organisms are heavier than 

 the medium. Occasionally small rumpled fragments of the pel- 

 licle remained at the top of the centrifuge tube, but these may 

 well have imprisoned air bubbles. 



Larson 1 has shown that this organism does not form pellicles 

 on media whose surface tension has been sufficiently reduced by 

 soap. The question naturally arises whether the diffusely grow- 

 ing organisms exhaust some surface tension depressant in the 

 media prior to their upward migration. This, however, is not 

 the case, since the surface tension remained approximately 59 

 dynes throughout the period of hourly observation (36 hours) 

 and was still the same 13 days after inoculation, at which time 

 the pellicles sank spontaneously. 



The avidity which this organism is supposed to have for 

 oxygen, is apparently not a factor, since cultures in large flasks 

 with oxygen bubbled up continuously from the bottom still ex- 

 hibit surface growth. 



A significant observation is that the upper surface of young pel- 

 licles is not wetted by water, although ethyl ether, petroleum 

 ether, and chloroform spread upon it readily. It is impossible 

 to invert a floating pellicle. If one lifts it and attempts to replace 

 it upside down on the water it at once rights itself and continues 

 to do so, until repeated manipulation has injured and wetted the 

 surface originally uppermost. In such a case the pellicle usually 

 slowly sinks. Experiments are now under way to determine 

 whether this behavior is due to an accumulation of old cells 

 storing lipoids in the upper layers of the pellicle. 



i Jour. Inf. Dis., 1919, xxv, 1. 



