OXYGEN CONSUMPTION OF OYSTERS 
499 
further by bubbling in carbon dioxide, 100 cubic centimeters of N/100 acetic acid were 
added. This brought the pH down to 6.0. It was difficult, however, to maintain 
this hydrogen-ion concentration for any length of time because the calcium carbonate 
of the shells acts as a buffer and brings it up to 6.4 very quickly. Table 9 embodies 
the results of this experiment. It indicates very clearly that oysters are not sus- 
ceptible to changes in hydrogen-ion concentration such as can be brought about 
under experimental conditions by their own metabolism. There was a noticeable 
decrease in the rate of oxygen consumption from pH 6.6 downward. 
Table 9. — Effect of decrease in -pH on oxygen consumption 
[Oyster No. 75] 
Date 
Time 
pH 
Oj ten- 
sion, 
c. c. per 
liter 
O 2 con- 
sumption, 
c. c. per 
liter per 
10 g. dry 
weight 
Remarks 
Date 
Time 
pH 
O 2 ten- 
sion, 
e. c. per 
liter 
O 2 con- 
sumption, 
c. c. per 
liter per 
10 g. dry 
weight 
Remarks 
10 so 
8 0 
4 520 
Sept. G_ _ 
12. 45 
6. 2 
3. 62 
CO 2 bubbled in. 
11. 00 
8.0 
4.448 
11. 60 
1. 15 
6.2 
3. 482 
4. 96 
11. 30 
7.9 
4. 000 
10. 07 
1. 45 
6.6 
3. 250 
2. 85 
10 9.0 
7 7 
4 21 
CO 2 bubbled in. 
Sept. 6_ _ 
2. 15 
6. 0 
2.658 
100 c. c. N/100 
10. 50 
7.7 
3. 74 
8. 15 
2. 45 
6. 1 
2. 550 
2.96 
acetic acid added. 
11.20 
7.7 
3.24 
9. 87 
3. 15 
6.3 
2. 470 
1. 766 
11 9.F, 
7 3 
3 00 
Do. 
Sept. 6-. 
3. 20 
8.0 
4. 51 
Fresh sea water. 
it 55 
7.3 
3. 15 
10. 16 
3.50 
8.0 
4. 270 
6.40 
12.25 
7.5 
2.85 
10. 84 
4.20 
7.9 
4. 00 
7. 95 
Sept. 6. - 
11. 35 
6. 6 
Do. 
12.05 
6.6 
3. 655 
8. 15 
12.36 
6.6 
3. 150 
10. 84 
The experimental data presented in Table 6 and Figure 4 show that below the 
oxygen tension of 1.50 cubic centimeters per liter the oxygen consumption began to 
decrease following the further decrease in oxygen tension. Because of the small 
number of observations and on account of considerable individual fluctuations in the 
metabolic rate, it is impossible at present to determine accurately the critical oxygen 
tension below which the consumption of oxygen by the oyster is proportional to its 
pressure. It is quite possible that critical tension is also subject to certain individual 
fluctuation. The dependence of the oxygen consumption on oxygen tension can be 
demonstrated, however, by an analysis of all the data obtained with various oysters, the 
metabolic rate of which was measured at various oxygen tensions. Such an analysis 
is possible because in all the experiments the temperature was kept constant and 
because, as has just been demonstrated, the fluctuations in the pH values between 
8.0 and 6.7 have no effect on the consumption of oxygen. An examination of Table 
10 shows that in the lower half of it (oxygen tensions below 2.5 cubic centimeters 
per liter) there is a definite correlation between the two variables, which in the upper 
half of the table (range between 2.5 and 4.5 cubic centimeters per liter) appear to be 
independent of each other. This relationship can be expressed in mathematical 
terms. First a coefficient of correlation using all the data as given in Table 10 was 
calculated. Then similar coefficients were computed using the data of oxygen con- 
sumptions obtained at the oxygen tensions between 2.50 and 4.5 cubic centimeters 
and between 0.0 and 2.49 cubic centimeters per liter. The results are as follows: 
Coefficient of correlation (all values) r = + .498 ± .048 
Coefficient of correlation (0 2 tension above 2.5 cubic centimeters) rj= +.146 + .102 
Coefficient of correlation (0 2 tension below 2.5 cubic centimeters) r 2 = + .646 +.046 
