193 



respiratory activity of the worms and, very probably, to a small ex- 

 tent, in the oxidation of their excretory products. Although the 

 data seem to show that the worms are sensitive to a lowering of the 

 dissolved oxygen content and that it is inimical to them, it does not 

 necessarily follow that the death of the worms was due to a com- 

 plete exhaustion of oxygen in the sample, since it was shown that it 

 sometimes occurred when considerable oxygen remained unconsumed. 

 For example, the water used in No. 6 of the above table, containing 

 at first 8.9 p.p.m. of dissolved oxygen, when tested at the end of 

 the experiment still contained 4.2 p.p.m. — a c|uantity which as the 

 initial content in one of the other experiments sufficed the worms for 

 98 hours. It was not possible in these experiments to remove the ex- 

 cretory products from the water and thereby eliminate the possi- 

 bility of this accumulating waste influencing the vital activities of the 

 womis ; but in an experiment made in another connection, a similar 

 quantity of worms were kept in 45 cc. of water in an open flask 

 and at the end of ten days all were alive and apparently as active as 

 at the beginning. Since in this last case the quantity of water was 

 so much smaller and the length of time so much greater than in the 

 above experiment it seems fairly certain that accumulating wastes 

 did not contribute in an important degree to the death of the worms. 

 Furthermore, the normal habitat is one in which organic wastes are at 

 a maximum. 



RELATION TO SEWAGE 



Relation to Crude Scivagc. — In another connection the fact was 

 brought out that no worms were found in the septic and settling 

 tanks, which receive the crude sewage. This was attributed chiefly 

 to the lack of dissolved oxygen. Tests were made by placing vig- 

 orous worms in bottles of crude sewage so corked that no air was 

 included or could gain access. Other tests were made by placing 

 wcM'ms in a flask which was about half filled with crude sewage, thus 

 leaving a large air space above the surface. In tests by the first 

 method the worms lived but 10 to 12 hours. Under the conditions 

 of the second test one lot lived 72 hours, which may be accounted 

 for by the absorption of air by the sewage from the air space above, 

 a limited oxygen supply being thus furnished for the worms. How- 

 ever since the sewage itself contained putrescible matter which also 

 drew heavily on the oxygen supply, the continued low oxygen con- 

 tent had a fatal effect. 



Behavior in the Presence of Sludge. — The following experiments 

 were performed in this connection : — Bxperiment i. A ground-glass 



