178 
BULLETIN OF THE BUREAU OF FISHERIES 
In experiments extended from July 19 to August 18, 7 oysters were subjected to 
a 1 -percent soluble fraction solution for from 18 to 24 hours. During this time 
the specific gravity of the laboratory sea water was very high, ranging from 1.0273 
to 1.0280 (17.5°). Water temperature averaged 27.6° C. 
The average rate of pumping during treatment, as compared with the rate 
before treatment, showed a reduction of 3.1 percent (table 11). This is insignificant 
by itself insofar as indicating any effect of 1-percent soluble fraction solution is 
concerned. However, this reduction in rate of flow is 15.6 percent lower than the 
control average during the treatment period. 
The greatest decrease in rate of flow resulting from this treatment was found 
in experiment 164, in which the reduction in rate amounted to 31.7 percent. This 
maximum effect was obtained with soluble fraction from a sample of oil washed 
25 times, the increase in specific gravity caused by washing being 0.0004. If the 
No urs after start 
Figure 7.— Effect of water soluble fraction on rate of flow of water. 
effect of the soluble fraction was owing to mineral salts* taken up from the oil by 
the sea water, it would be expected that the inhibiting power of the soluble fraction 
on rate of flow would gradually diminish as the salts were exhausted, and that the 
increase in specific gravity of the sea water after washing with oil would likewise 
decline. However, this was not the case and the inhibiting effect of the oil extract 
did not diminish with subsequent washing of the sample. 
Except for experiment 164, the effect of treatment with 1 percent soluble fraction 
gives percentages closely comparable with similar figures for the control experiments. 
However, considering the orderly decrease in rate of flow caused by treatment with 
increasing percentages of soluble fraction, it is believed that a 1 percent soluble 
fraction exerts a definite though slight inhibiting effect on the ciliated epithelium 
of the gills. 
Seven experiments were made with 5 percent soluble fraction solution between 
June 21 and September 5. The average temperature was 26.8° C., and the specific 
