191 



A series of samples of tap \Yater whose dissolved oxygen content 

 rang-ed from 1.2 p. p.m. to 9.2 p. p.m. was used as a medium. The 

 highest dissolved oxygen sample (9.2 p. p.m.) was obtained by agitat- 

 ing the water in air. Tests were also made in which the medium was 

 the sprinkling- filter effluent, its dissolved oxygen content varying from 

 10 to 13 p.p.m. Samples with the lower dissolved oxygen content 

 were procured either by mixing boiled tap water with different quanti- 

 ties of ordinary tap waiter or by boiling a considerable quantity of tap 

 water and allowing it to stand in an open vessel, samples being taken 

 at successive intervals as the water gradually absorbed oxygen from 

 the air. Sampling bottles of 128 cc. corrected capacity were used, 

 and care was taken that each was so stoppered that no air bubbles 

 were included. Two samples of each of the different grades of water 

 were taken, one being used for the worms and the other for the de- 

 termination of the dissolved oxygen content. Ten vigorous worms, 

 fresh from the filters, were quickly transferred to one of the bottles 

 and the time noted. The worms were thoroughly cleaned before they 

 were put into the bottles. This procedure was followed for each of 

 the series of samples taken. The bottles were all kept under condi- 

 tions which simulated those existing in the sprinkling filter and were 

 observ-ed frequently. 



It might appear that a source of error existed because no account 

 was taken of the carbon dioxide and the nitrogen in the samples. 

 When water is boiled it loses most of the dissolved oxygen, nitrogen, 

 and carbon dioxide, and when oxygen was added to the samples by 

 exposure to the air or by the addition of ordinary tap water, certain 

 quantities of nitrogen and carbon dioxide were also added. However, 

 the writer believes that this source of error did not interfere with 

 the essential results of the experiments. The carbon dioxide in the 

 sprinkling filter is an extremely variable quantity, since much of the 

 gas must be lost when it is sprayed out into the air, and consequently 

 the liquid coming to the worms probably contains but small quan- 

 tities of carbon dioxide — a condition comparable to that in the sam- 

 pling bottles of the experiments. Only a very limited amount of ni- 

 trogen (dissolved) is present in the sprinkling filter influent. When 

 the tap water, which contained a certain quantity of nitrogen, was 

 boiled the major part of the nitrogen was lost. In those samples made 

 up by mixing the boiled and unboiled tap water some nitrogen was 

 added with the latter, while in the samples made by exposure of the 

 boiled water to the air nitrogen was taken up from the air very slowly, 

 so that in all cases the samples closely approximated the conditions 

 in the sprinkling filter. Of the three gases involved the oxygen was 



