404 ANN BISHOP 



well. Later, the addition of hay infusion was found to be 

 imnecessar3% 



The tubes were allowed to stand for not less than four days 

 at a constant temperature of 20° C. or for a longer period at 

 a lower temperature in order that bacteria might multiply 

 and decomposition of the leaves and debris set in. Each tube 

 was then inoculated with a few Spirostoma. 



In order to discover whether any one particular kind of leaf 

 is more suitable for the cultivation of these animals than 

 another, cultures were made of oak leaves, beech leaves, 

 rushes, and leaves of potomageton respectively. It was found, 

 however, that no individual leaf gave such good results as did 

 a mixture of several different kinds. 



At first no multiplication of the Spirostoma took place, 

 although in the majority of the tubes the animals remained 

 alive. After a week had elapsed a smell of decay, in which 

 the odour of sulphuretted hydrogen could be detected easily, 

 issued from the tubes. The cultures darkened in colour, and 

 in a number of cases microscopical investigation revealed the 

 presence of Beggiatoa and numbers of minute green flagellates. 

 The Spirostoma then began to increase rapidly until, about 

 a month after the making of the cultures, they were present 

 in large numbers. 



A comparison of these cultures with the ponds in Which 

 Spirostomum ambiguum is numerous seems to show- 

 that by this method conditions approximately similar to those 

 of their natural environment are obtained artificially. The 

 odour of sulphuretted hydrogen, so noticeable when collecting 

 in the type of pond in which Spirostomum ambiguum 

 is numerous, evidently arises from the decaying vegetable 

 matter. Lauterborn (14) believes its presence to be charac- 

 teristic of the environment necessary to what he calls a ' sapro- 

 pelic ' fauna , and S p i r o s t o m u m a m b i g u u m figures in 

 his list of such sapropelic organisms. 



There seems to be a direct relation between the presence 

 of sulphuretted hydrogen and a thriving condition of the 

 Spirostoma. When the amount of sulphuretted hydrogen is 



