EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
191 
ments are not considered to be significant insofar as the oil pollution problem is 
concerned, and are included here only for the sake of completeness. 
The experiments with bleed water show that it contains a substance or substances 
inhibiting the work of the ciliated epithelium. The action becomes apparent at a 
concentration of 10 percent brine in sea water. The toxicity increases in proportion 
to the increase in concentration. This is apparent from an examination of figure 10, 
in which the average depression in rate of flow of water through the gills, expressed 
in percentage of the normal, is plotted against the concentrations. 
EFFECT OF CONSECUTIVE TREATMENTS 
In the experiments described above the oysters were treated for a veiy short 
period of time lasting only a few minutes. The question arises as to whether or not 
as a result of a more prolonged exposure, they may become adapted or develop greater 
tolerance to the toxic substances present in crude oil and bleed water. 
As stated previously, the drop counting technique is not adapted for experimenta- 
tion over a period of more than 2 or 3 days. Several experiments were made in 
which the same oyster was treated with oil extract or bleed water several times 
within this period. 
Five oysters w T ere used in a total of 16 experiments. The results are summarized 
in table 19. Thirteen of these experiments have been analyzed to determine the 
effect of 2 or more treatments. 
Table 19. — The effect of consecutive treatments with soluble fraction of oil and bleed water on the rate 
of pumping by the gills of the oyster 
Experiment no. 
Date 
Test solution 
Percent 
of solu- 
tion 
Effect of 
treatment 
Length of 
treatment 
Temper- 
ature 
60 
100 
Percent 
119. 6 
Minutes 
5 
° c. 
13. 6 
60A 
100 
62.8 
5 
15. 0 
63 
10 
90.0 
5 
17. 3 
63A 
100 
82.0 
5 
17. 4 
63 B 
Bleed water 
10 
73.0 
5 
15.2 
65 
33 
94.0 
10 
15. 0 
65A 
Soluble fraction _ 
100 
112.7 
5 
14.8 
65 B 
Dec. 8 
40 
41.0 
10 
14. 1 
65C 
do 
10 
106.0 
10 
17. 1 
65D 
20 
91. 0 
10 
15. 2 
78 
May 14 
Soluble fraction 
100 
9.2 
8 
22. 1 
79 
do 
100 
14.0 
8 
22.4 
80 
100 
18.5 
8 
23.3 
81 
May 15 
do__ 
100 
60.3 
8 
22.9 
82... 
100 
64.0 
8 
22. 5 
83 
do__ .. 
100 
26.2 
20 
22.3 
Oyster no. 60 was used in two experiments, 60 and 60A. The duration of treat- 
ment with soluble fraction from Barre oil was 5 minutes in both. Five hours elapsed 
between treatments. The difference in temperature at the beginning of the 2 experi- 
ments was 1.4° C. In experiment 60, the rate of pumping was accelerated almost 
20 percent above normal, wTdle in 60A there was a reduction in rate of about 37 
percent. 
Oyster no. 63 was used in experiments 63, 63A, and 63B. Bleed water was used 
in 63 and 63B, and soluble fraction from Barre crude oil in 63 A. Two hours elapsed 
between 63 and 63A. 63B was made the following day, 18 hours after 63A. The 
duration of treatment was 5 minutes in each. 
