206 
BULLETIN OP THE BUREAU OP FISHERIES 
discrepency between the two sets of experiments may be due to the difference in 
technique or to the better condition of North Carolina oysters used in Prytherch’s 
experiments. 
In another set of laboratory experiments no higher mortality than that in con- 
trols was observed among the oysters which, over a period of 6 to 8 weeks, were im- 
mersed at regular intervals in oil (table 3, p. 163). In some of the experiments the 
mortality among the controls was as high as 50 percent, indicating unfavorable labo- 
ratory conditions under which the animals were kept. It is possible that these 
conditions beclouded the effect of oil on oysters. 
The fact that oysters survived the treatment with oil does not indicate that they 
were not affected by it. Analyses made by Galtsoff show slight decrease in glycogen 
content of oysters kept in the laboratory in the oil-polluted water (table 4). The 
result may be due either to the disturbance in the functioning of the feeding apparatus 
of the organism or to the decreased supply of food. 
A regular operation of the muscular mechanism involved in closing and opening 
of the shell is prerequisite for the normal feeding of the oyster. Two sets of experi- 
ments, carried out by Prytherch in 1933 and Galtsoff and Smith in 1934, gave identical 
results showing that the presence of oil has no effect on the mechanism of the adductor 
muscle. 
In the first set of experiments, continuous kymograph records were obtained of 
5 oysters which were kept under observation for 3 months. The average number of 
hours per day the oysters were open was 11.2 for the controls and varied between 10.0 
and 13.6 for the experimental oysters. In the second set of experiments, 6 control 
oysters kept under observation from 4 to 14 days, were open on the average of 10.5 
hours daily, whereas the average figure for 10 experimental oysters kept under ob- 
servation from 4 to 8 days, was 9.6 hours. In both cases the difference is insignificant. 
Although the presence of oil in the sea water does not reduce the number of hours 
the oyster keeps its shell open, and therefore the duration of feeding of the mollusk 
is not decreased, the rate of feeding is easily affected by the presence of polluting 
substance. As the feeding of the oyster is primarily dependent upon the amount of 
water passed through the gills, the rate of pumping of water can be used as a measure 
of the rate of feeding. The results of the experiments in which the cone method, 
previously described by Galtsoff (1928) was used, and of those in which the drop 
counting technique was employed (fig. 5), show that crude oil contains substances 
soluble in the sea water which produces anaesthetic effect on the ciliated epithelium 
of the gills. The inhibiting action is not due to the mineral salts that may be leached 
out in preparing the water soluble fraction of the sample of oil by shaking it with sea 
water. It is apparent that certain organic compounds of oil are slightly soluble in 
sea water. This conclusion can be drawn from the observations that after 28 washings 
with water, the sample of oil did not lose its toxic property and yielded extract, the 
anaesthetic potency of which was equal to those obtained with the first washings. 
The inhibiting effect of the water-soluble fraction is proportional to its concentration 
(figs. 6, 7, 8, and 9). From a large number of experiments summarized in these figures 
and tables 11, 12, and 13, the inference can be drawn that a concentration between 
20 and 30 percent of the soluble fraction will, on the average, reduce the rate of feeding 
of the oyster to one-half of its normal value (fig. 8). 
Under the conditions of the experiments, the recovery of the ciliary motion 
following the removal of the oil extract, was almost complete. Inasmuch as the 
