175 



In small coiu-cntratinns, liulovv 10 jiarts per millicin, (ir practically the [)oint 

 where the odor of chlorine oxer the solution becomes noticeable, the teredos con- 

 tinued to feed, seemingly Luiharnied. It must be remembered that in maintaining 

 even these small concentrations of chlorine, consideralile amounts will be gi\en off 

 into the surrtjunding atmosphere. At higher concentrations the siphons were always 

 immediately withdrawn. However, after the highest concentration used (120 parts 

 per million) applied for the longest time tried (72 hours), on the stick being placed 

 in fresh sea water (chlorine free) the borers again extended their siphons and were 

 apparenth' none the worse for their experience. This concentration of 120 parts per 

 million was sufficient to give oft into the air enough of the gas to make human Ijreathing 

 ver\' uncomlortable. 



Table 24 gi\es a summary of the experimental data. At the end of the series, 

 the teredos in all aquaria were apparently in good health, and there were as many 

 active siphons as at the beginning. Some of the borers lived f(jr several months, 

 even under the unfavorable conditions of the acjuaria. The borers in one of the pieces 

 subjected to the chlorine treatment lived longer than those in the control piece, 

 which had had no chlorine treatment. 



*After each chlorine exposure, the block was placed in fresh bay water for 24 hours, 

 tp.p.m. = parts per million. 



Undoubtedly the chlorine was offensive to the borers. When it was added slowly, 

 the siphons were retracted progressively along the wood in the direction in which 

 the chlorine spread through the water. Furthermore, when the infested pieces were 

 taken out of fresh bay water, exposed to the air for a moment and put back into the 

 water again, the teredos extended their siphons and began to feed again after a very 

 few minutes. On the other hand, if they were put into a solution giving a noticeable 

 odor of chlorine, they did not extend their siphons again. They were never found 

 feeding in concentrations as great as 10 parts per million. The concentration of chlorine 

 used in several of the experiments might, therefore, ha\-e been toxic to the teredos. 



