192 
BULLETIN OF THE BUREAU OF FISHERIES 
Comparing the effect of the two treatments with bleed water, it will be noted 
that the second treatment reduced the rate of flow 27 percent as compared with a 
10-percent reduction for the first treatment. The interval between these treatments 
was more than 20 hours. The difference in temperature at the beginning of these 
experiments was 2.1° C. 
Oyster no. 65 was used in 5 experiments, 4 with bleed water (65, 65B, 65C, and 
65D), and 1 (65A) with soluble fraction from Pelto crude oil. Nos. 65 and 65A were 
made on December 7, with a 3-hour rest period between. The other three experiments 
were made the following day. The intervals between these experiments are 
65A to 65B, 18 hours; 65B to 65C, 2.5 hours; 65C to 65D, 50 minutes. Com- 
parison of the effects of several treatments in this case is difficult because a different 
concentration of bleed water was used in each. However, it will be observed that 
the final treatment (65D) with 20 percent bleed water was of the same order of 
effectiveness as the first treatment with 33 percent bleed water. The time of treat- 
ment was 10 minutes in both experiments, and the temperature at the beginning 
of each was practically the same. 
Experiments 78, 79, and 80 were made with the same oyster, using the soluble 
fraction from Barre crude oil. The duration of treatment was 8 minutes for each 
and the temperature difference was negligible. Twenty minutes elapsed between 
78 and 79; 3 hours elapsed between 79 and 80. The average reduction in rate of flow 
during treatment as shown in table 19 is 90.8 percent for experiment 78, 86 percent 
for experiment 79, and 81 .5 for experiment 80. Thus it would appear that succeeding 
treatments were not so effective as the first. However, it will be remembered that 
the figures in this table are prepared to show only the average effect during the period 
of treatment, which is considered to be the actual interval during which the test 
solution flows over the oyster plus an additional 10 minutes for replacing the test 
solution with fresh sea water. A detailed analysis of the records shows that while 
the initial reduction in rate of flow is greater in the first experiment, and consequently 
tbe average reduction appears to be greater, yet the period of no current is 20 minutes 
in the second experiment and only 15 minutes in the first. Actually, tbe second 
treatment exerted a retarding action on tbe pumping activity of the cilia for a longer 
period than was the case in the first experiment. These remarks apply also to the 
third experiment, no. 80. The initial depressing effect is not so great, as in no. 78, 
and tbe period of no current is only 15 minutes, but this period begins after the test 
solution has been turned off, and subsequent recovery as evidenced by the average 
rate of flow will be seen to take place more slowly than in either of the preceding two 
experiments. 
Experiments 81, 82, and 83 were made the same day with the soluble fraction 
from Barre crude oil. The interval between treatments is approximately 2 hours 
for experiments 81 and 82. Two and a half hours elapsed between treatments in 82 
and 83. The duration of treatment was 8 minutes in the first two and 20 minutes 
in tbe third experiment. Tbe latter, therefore, cannot be compared directly with 
the others. 
Oyster no. 81 used in these experiments had the highest rate of pumping in the 
series and had a high resistance to treatment with soluble fraction. The reduction 
in rate of flow caused by the test solution was 39.7 percent in experiment 81 and 36 
percent in 82. The average rate at 5-minute intervals as given in table 14 does not 
show an appreciable difference in effectiveness of the soluble fraction for the two 
experiments. 
