EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
189 
study of recovery was not considered to be of sufficient importance to the problem 
to warrant additional time. 
The effect of treatment obtained by dividing the average rate during treatment 
(col. 4) by the average rate before treatment (col. 3) multiplied by 100 is a measure 
of the toxicity of the test solution. However, this value sometimes masks the actual 
effects of the test solution, and for this reason each experiment is presented com- 
pletely in table 18, in which the average rate of flow in drops per minute is shown for 
each 5-minute interval. The intervals in which the test solution was flowing are 
indicated in bold face type, the figure in the last column giving the actual number of 
minutes during which the bleed water was running into the experimental chamber. 
An example of the masking of brine effects as shown in column 6, table 17, is 
experiment 55. In this table the reduction in rate of flow due to a 10-minute treat- 
ment with 10 percent bleed water solution is 5 percent. An examination of the actual 
figures in table 18, shows that during the first 5 minutes of treatment there was an 
accelerating effect of about 16 percent; during the second 5-minutes of treatment the 
rate fell to nearly normal ; in the 5-minute period immediately succeeding treatment, 
the flow decreased 36 percent, and returned to normal in the next 5-minute interval. 
The effect of bleed water in experiment 55, therefore, consists of an initial acceleration 
in ciliary activity followed by a considerable inhibition. 
Of the 5 experiments using approximately 10 percent bleed water solution, 3 
(nos. 55, 63, and 63B) show a reduction in rate of flow during treatment, the other 
2 having an increased rate of pumping. It was to be expected that similar to the 
action of various poisons the low concentrations of bleed water may have a stimulating 
effect at least in some of the individuals. 
Owing to large individual differences in condition and resistance of oysters, it is 
impossible to establish an exact concentration level for bleed water solutions, above 
which the rate of pumping would always be reduced, and below which an increase in 
rate would occur. However, the rate of pumping in the 10 percent bleed water group 
is reduced an average of 5 percent, which seems to indicate that this concentration 
slightly exceeds the limit of tolerance. 
Four experiments were made using 20 percent bleed water. These show a 
decidedly greater depressing effect, the average rate of flow during treatment for the 
group being only 86.5 percent of normal. This increase in depressing effect of the 
20 percent bleed water probably is due to a greater proportion of ions affecting the gill 
cilia, for there was no increase in the specific gravity of the solution as compared with 
laboratory sea water. On the contrary it will be seen (table 17) that the specific 
gravity of the test solution in experiments with 20 percent bleed water is closer to 
that of the laboratory sea water than is the case in the experiments with 10 percent 
bleed water. 
The effect of 33 percent bleed water solution is shown by three experiments (nos. 
65, 53, and 53 A). In two experiments (65B and 53B) 40-percent bleed water was 
used. The average reduction in rate of flow resulting from a 10-minute treatment 
with these concentrations of bleed water was 32.6 percent. 
One experiment each was made with bleed water concentrations of 50, 60, 80, 
and 100 percent. There is comparatively little difference in the effects of these con- 
centrations during treatment for 10 minutes. However, the length of time during 
which no water was pumped through the gills increases steadily, from 10 minutes 
in the case of 50 percent bleed water to more than 2 hours for 100 percent. The 
