SPIROSTOMUM AMBIGUUM 405 



very great the Spirostoma die. Whether the Spirostoma are 

 directly dependent upon the sulphuretted hydrogen or upon 

 some product of protein decomposition during which sul- 

 phuretted hydrogen is liberated, or whether the kind of 

 bacteria upon which they flourish best is dependent upon it, 

 I am at present unable, to determine. The last supposition, 

 however, seems the most likely. 



While these experiments were being made excellent cultures 

 of Amoeba proteus were being obtained by Sister Monica 

 Taylor's wheat method (29). Since large ciliates were often 

 plentiful in such cultures it seemed probable that Spiro- 

 stomum ambiguum might be grown in a similar medium. 

 To test this assumption, two wheat grains, boiled to stop 

 germination, were put into a test-tube, which was then filled 

 up with aquarium water, previously boiled to free it from 

 any living organisms. The tubes were allowed to stand in 

 the incubator at a temperature of 20° C. from four to five 

 days to favour the development of a thick bacterial growth. 

 Spirostoma were then added. Excellent results were obtained 

 from this method, thicker cultures being obtained than from 

 the former cultures. In addition to the Spirostoma, Chilo- 

 monas, green flagellates, and pink bacteria often developed 

 in these cultures. The wheat cultures are not only easier 

 to prepare, but have the additional advantage that the bacterial 

 food-supply of the ciliata, and therefore the cultures themselves, 

 lasts longer than it does in the leaf-extract medium. 



It is interesting to note that long, narrow test-tubes seem to 

 be necessary for the success of these cultures. All attempts to 

 cultivate Spirostomum in either leaf or wheat extract in 

 shallow, wide dishes were unsuccessful. Spirostomum evidently 

 thrives best in deep water where the surface area, and therefore 

 the amount of dissolved oxygen, is small. That it was not the 

 shallowness of the medium which killed the cultures was shown 

 by attempting to grow Spirostoma in wide, deep jars, when 

 the result, or rather the lack of result, was the same as in the 

 case of the wide, shallow dishes. 



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