450 PROCEEDINGS OF THE AMERICAN ACADEMY. 



ing of adjustment, furnished the most successful starting points for mass- 

 culture. 



The original cultures were obtained by collecting a variety of solid 

 material from the edge of ponds in the vicinity of Cambridge. The col- 

 lection must not be too rich in fermentable matter. If this precaution is 

 not observed, such Stentors as are brought in with it will be killed off 

 by an excess of the initial fermentation characteristic of every culture. 

 Brown leaves and dead reeds were found most useful. Both in artificial 

 and in natural cultures decaying cellulose proved to he the hest source of 

 the food supply for Stentor. It is of course only the source, not the food 

 itself. An excess of fleshy green matter must be avoided, but some 

 thread algae may be included. No more pond water need be taken than 

 is necessary to cover the collection. It is best to transfer the solid 

 matter to a jar while the latter is in the water. It was customary to 

 set mass-cultures, whether natural or artificial, in cylindrical glass jars 

 of about 4000 cc. capacity. The object in using such large vessels was 

 to obtain cultures whose longevity would be great in proportion to the 

 food supply. To each jar was transferred enough of the collected matter 

 to occupy about one tenth of its volume. The jar was then filled with 

 tap water and kept at room temperature, or if convenient a little warmer. 

 Jars should never be allowed to cool to low temperature, should be 

 covered with a pane of glass to prevent evaporation, and should stand in 

 diffuse daylight. Provided Stentors are originally present, some of these 

 cultures will be successful, and after one or two weeks will show a growth 

 of Stentors localized on the side of the jar away from the light. If too 

 much fermentable material was present, it will take longer for the culture 

 to develop, because Stentors will not appear in abundance until after the 

 initial fermentation has ceased. In some cases a culture develops after 

 weeks of standing. The above procedure, although frequently successful, 

 carried with it no certainty of result and hence pointed to the necessity 

 of a further study of conditions. Cultures were set with an abundant 

 supply of oxygen-producing water plants, in addition to the leaves and 

 reeds above mentioned. The result was signal failure. This fact, coupled 

 with the observation that many successful cultures contained no evident 

 abundance of algae, shows that the experimenter need take no special 

 precautions to supply oxygen to a Stentor culture. The decaying algae 

 frequently noticed in good cultures probably acted as a source of food. 



Observations were made to determine directly the immediate food of 

 Stentor. The animals were compressed under a thin cover glass by 

 gradually withdrawing the liquid medium with filter paper. Their 



