192 



the only one which was varied widely in the experiments. Other 

 workers have found that it is very difficult, in fact almost impossible, 

 by methods known at present to vary absolutely a single gas in this 

 kind of experimentation, and thus a small source of error indubi- 

 tably exists. It is thought, however, that in this case it may be 

 practically negligible, since the sole aim of the experiments was to 

 determine the general effect of a decreased supply of oxygen on the 

 worms. 



The dissolved oxygen content of each sample was determined by 

 using Winkler's method as outlined in "Standard Methods of Water 

 Analysis", 191 2. Briefly stated, a solution of manganous sulphate 

 was added to the sample and followed by an alkaline solution of 

 potassium iodide. The precipitate of manganous hydrate was allowed 

 to settle. Sulphuric acid was then added, and the free iodine in the 

 solution was titrated with a standardized solution of sodium thiosul- 

 phate. The equivalent of free iodine was calculated to oxygen and 

 the results expressed in parts per million. 



The following tabular exhibit of the results of one of the experi- 

 ments will serve as a representative of other, similar ones made in 

 this connection. 



The data of the other experiments carried on in this connection 

 varied in detail to some extent from the preceding, but the general 

 showing was the same, namely, that it is indispensable to the well- 

 being of these worms that they should have oxygen in considerable 

 cjuantities. To judge fairly concerning the deleterious effect of reduc- 

 ing this normal requirement, as in these tests, it is necessary to keep 

 in mind the fact that in each of the samples the water gradually be- 

 comes poorer in oxygen since it was constantly being used in the 



