EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
177 
sea water from day to day, and this factor is not believed to have affected the results. 
In most experiments the specific gravity of the test solution was brought within 
±0.0002 of the specific gravity of the laboratory sea water so as to avoid stimula- 
tion by salinity changes during the course of an experiment. Complete data of the 
specific gravity of the laboratory water and of the solution of soluble fraction used 
in the experiments are given in the table. 
Fluctuations in temperature may be disregarded insofar as they might influence 
the results obtained with different concentrations of soluble fraction. The maxi- 
mum difference in average temperature between the several groups of experiments 
is 0.9° C. This comparatively slight variation was made possible by using 4 sets 
of apparatus at a time so 
arranging to have a differ- 
ent concentration of soluble 
fraction in each tray, the 
experiments at various con- 
centration levels were car- 
ried along together so that 
seasonal changes in tem- 
perature did not affect one 
group of experiments more 
than another. Tempera- 
ture fluctuations during the 
course of individual experi- 
ments were usually less 
than 2° C. 
In 5 of the controls 
(table 11) the rate of flow 
increased slowly during the 
course of the experiments. 
Two others showed a very 
slight decrease in rate, and 
in 1 experiment (no. 121) 
in which there was no aera- 
tion or circulation of water 
the decrease amounted to 
11.8 percent. The charac 1 
teristic gradual increase in 
rate of pumping is attri- 
buted to recovery from the 
mechanical stimulation of the plugging operation. The controls cover the period 
from June 5 to August 29, and except for the first experiment, no. 92, all were sub- 
jected to the same range of salinities and temperatures as the experimental oysters. 
On the average for all the 8 controls there was an increase in the velocity of cur- 
rent which amounted to 12.0 percent. The average duration of test for controls 
was 34 hours; for experimental oysters, 20.5 hours. The total elapsed time during 
which each oyster was plugged averaged approximately 6 hours more than the 
duration test. 
that 4 experiments could be run simultaneously. By 
Figure 6.— Effect of water soluble fraction on rate of flow of water. Exp. 178. 
