is advanced only as one of the possibilities, for other faotors, such, 

 for instance, as the changes in the concentration of microplankton or 

 the presence of the products of plankton metabolism may either suppress 

 or stimulate the rate of pumping of water by the oyster. The sex of 

 oysters used in the tests is not known for, when they were examined at 

 the completion of the experiments in September, the gonads were in an 

 indifferent phase and the sex was unidentifiable. 



In a third experiment (table 23) conducted from August 4 to 17, 1948 

 after the spawning of oysters had been ocmipleted, the interfering factor 

 was absent and the depressing effect of oil was more pronounced, as can 

 be seen by examining figure 17. 



Regardless of the temporary increases, in all instances the rate 

 of pumping of water by the oysters kept in oil-contaminated water was 

 reduced in comparison with that of the controls. 



Other significant changes affecting the physiology of the adductor 

 muscle became apparent as the exposure in oil-contaminated water 

 continued. The shell movements were greatly decreased, and the oysters 

 remained open for a long time without changing the position of the valves. 

 This abnormal behavior of the adductor is clearly seen in figure 18. In 

 many instances no water was pvmiped by the gills, although the shells 

 remained wide open* These symptons are obvious signs of the wesJcening 

 of the neuro-muscular and ciliary systems of the oyster. Qi contrast 

 to the experimental oysters, the controls at the same day of the experi- 

 ment showed normal behavior at the very end of the experiment and the 

 rate of punping was sometimes even greater than at the start (figure 19K 



Toward the end of the first and second experiments, the supply of 

 water was reversed and oil-oontamlnated water was diverted to the controls, 

 while the experimental oysters were given pure water. This change is 

 indicated in the graphs (figures 12 and 13) by vertical arrows. No recovery 

 in the rate of pianping was observed in the first experiment but there was a 

 marked decrease in the rate of pumping in the control. In the second 

 experiment (figure 13) there was some reoovery in the oil-treated oyster 

 and a marked decrease in the rate of pumping in the control. 



These observations confirm our findings that sea water iriiich was 

 allowed to flow over cxnide oil botmd by carbonized sand contained a certain 

 toxic substance or substances which impede the ciliary activity of the gill' 

 epithelium and interferes with the normal behavior of the adductor muscle. 

 We also infer from experiment No. 2 that after 28 days in running sea water 

 the crude oil and sand mixture still retained its toxicity* 



43 



