readings, expressed as the rate of cvirrent of water in mm* per second, 

 were plotted against time. 



In the first test 20 ml. of Diesel oil were used, which gave the 

 ratio of one part of oil to 250 parts of sea water* The results, plotted 

 in figure 3, clearly indicate a marked depression in the rate of current, 

 which reaches its maximum about one hour after the introduction of oil. 

 It is significant that the rate of current of water in the control 

 oysters gradually increases, while in both experimental oysters it is 

 materially depressed. We conclude from these observations that oil contains 

 substances which, after being leached by water, exert a depressive effect 

 on the ciliated epithelium of the oyster. 



To corroborate this inference we prepared an extract by shaking a 

 sample of Diesel oil with 8ui ecfual volume of sea water and tested its 

 effect. The mixture of oil and sea water was poured in a large Erlenmeyer 

 flask with only sufficient air space to allow good agitation and shaken 

 for three hours on each of three succeeding days. Then the sample was 

 transferred to a large separatory funnel and, after separation of the oil 

 and water, the transparent and colorless water fraction was withdrawn and 

 used in the desired concentration. As can be seen from figure 4, 10 percent 

 had no effect, slight reduction was caused by 20 percent, while very marked 

 depression occurred in the concentrations of 30 and 50 percent. 



Because of the known greater toxicity of crude oil, only 200 ml. in 

 four liters of sea water were used in preparing an extract. The sample 

 was shaken for five hours and then allovj^ed to separate overnight. Marked 

 depression in the rate of cloacal current was produced in the concentra- 

 tions of 50 and 20 percent of this extract (figures 5 and 6). 



In a second test, the oil was used in a ratio of one part to 100 

 parts of sea water. The mixture was poured into a carboy and, allowed to 

 stand for six days i during this time it was aerated by streams of fine 

 air bubbles whioh kept the oil agitated. No reduction in the rate of 

 current was noticed in the samples containing 30 and 50 percent of this 

 extract (figures 7 and 8)« 



36^ 



