238 Papers from the Department of Marine Biology. 



was measured to the nearest tenth of a degree and maintained to within 

 0.2° of 30°. 



The sea surface is at about the optimum pH for metabolism (usually 

 8.1 to 8.3), but the variation in metabolism with variation of pH within 

 the range studied is very slight, as shown by table 13 (diameter of 

 cassiopea = 10 cm.). 



These variations in oxidation may be due to experimental errors and 

 variation in O2 concentration, except the first two, which show a slight 

 lowering of oxidation when the pH is re- 

 duced to about 7.5. Table 14. 



In comparing the rise in temperature in 

 the calorimeter with that calculated from 

 the O2 consumption, the assumptions were 

 made that the respiratory quotient was 

 0.95, and that a certain mixture of pro- 

 teins, fats, and carbohydrates was burned, 

 giving 6 gram-calories per cubic centimeter of CO2, as in table 14. 



In these experiments it was assumed that there was no loss of heat, 

 although some heat must have passed into the thermometer bulb and 

 glass lining of the thermos bottle. The specific heat of the sea-water 

 and the cassiopea was taken as unity because the determinations were 

 not accurate enough to warrant the application of small corrections. 

 The experiments had to continue for 2 hours in order to obtain an accu- 

 rately measurable rise in temperature, and the tedium of keeping the 

 tank at the same temperature as the calorimeter necessitated the 

 substitution of indirect calorimetry in the remainder of the experiments. 



Some preliminary experiments to show the effect of O2 tension are 

 shown in table 15. Since the temperature was constant, the O2 tension 

 is proportional to O2 concentration. 



Average O2 concentration 11.9 1.91 :: 3.36 1.55 



O2 consumption 2.6 2.38 :: 2.26 1.65 



In performing these experiments, a number of possible sources of 

 error were thought of and it was decided to make a more detailed study 

 of the metabolism of Cassiopea before returning to the subject. The 

 chief danger of error was in prolonging the experiment until all of the 

 O2 was used up. It was found that Cassiopea could live more than 7 

 hours without oxygen, in which case no measurable quantity of CO2 was 

 produced. Vernon observed practically no increase in the respiratory 

 quotient of jelly-fish correlated with oxygen-want, whereas the respira- 

 tory quotient of fishes increased under these conditions. 



In order to determine whether the rate of oxidation depends on the 

 oxygen tension, it is desirable to know something about the oxygen 

 tension inside the living cells. In other words, the transfer of oxygen 

 to the cells must be facilitated as much as possible if we are to judge 

 anything about the tension of O2 within them from that in the sea- water. 



