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 02 was used up. It was found that Cassiopea could live more than 7 hours without oxygen, in which case no measurable quantity of 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 02 within them from that in the sea-water.
This could be approximated by agitating free cells or a single layer of cells with the water or circulating the water over a single layer of cells. When using free cells, some are liable to injury and more or less disin tegration, thus interfering with the titration, but, notwithstanding the criticism of Heilbrunn, comparative results may be obtained (Mc Clendon and Mitchell). Cassiopea was chosen because the cells are spread in thin layers on the surface of a mesoglea which will be shown to use practically no oxygen. The pulsations of a cassiopea bring cur rents of water over the cell-layers, so that diffusion is necessary only for a minute distance. The error due to this diffusion would be large only when the tension is very small. By skillful manipulation, the mucous secretion may be prevented from increasing or leaving the surface of the cassiopea.
Evidence that oxidation is confined to the cell-layers is apparent in the fact that oxidation is not proportional to the volume but to the surface. It would be practically impossible to measure the surface, but since the individuals are practically of the same shape, the surface is proportional to the square of the diameter. Since Cassiopea is elastic, the diameter was always measured under the same conditions, i. e., resting on a glass plate, with the exumbrella in contact with the glass (and the average of 2 diame ters at right angles to one another taken). Some
rough preliminary determinations showed the con sumption in cubic centimeters per hour to be about 0.023 time the square of the diameter in centimeters, as shown in table 15. Very small cassiopeas used more than calculated from the formula (an anomaly which is correlated with more rapid pulsa tions). A cassiopea 3.5 cm. in diameter pulsated once a second, whereas one 10 cm. in diameter pulsated 0.3 time per second. In order to compare experiments on Cassiopea where the weight is recorded, it is convenient to know that the diameter is cm. = weight in grams.
Table 16 gives the respiration-rate under different conditions, except that the temperature is always 30°.
In this table the pH and per liter at the beginning of the ex periment are given; the pH was about 0.09, while the was 1.5 c.c. lower at the end of each experiment. The average during each experiment influences the used per hour, but apparently no difference in the quotient of the used per hour divided by the square of the diameter can be correlated with difference in size. Using greater extremes of size, however, the quotient seems to decrease as the diam eter increases, and therefore extreme sizes were usually avoided after this was discovered.
All of the experiments were made under conditions of starvation, and hence the cassiopea used its own substance as a source of energy. Starvation can hardly be considered a pathological process in Cassiopea, however, since it may remain alive for months without food, constantly decreasing in weight until it almost disappears before death. Mayer (1914) determined the loss in weight as about 5.6 per cent per day at about 30°, although no thermostat was used. If y is the weight at any moment and w is the weight when starvation commenced and n is the number of days of starvation, y=w(1-0.056)* Since I found the diameter to be 2.25 times the cube root of the weight, if the weight were 100 grams, the diameter would be 10.45 cm. The 02 consumed during one day would be about 0.023 time the square of the diameter times 24 = about 60 c.c. 02 absorbed and 57 c.c. given out. If we assume that protein was burned and that 5.9 gram-calories correspond to 1 c.c. the metabolism would equal 336 gm. cal. for the day. If we assume that a certain mixture of pro teins, fats, and carbohydrates was burned and 6 calories correspond to 1 c.c. of the metabolism would equal 342 calories per day.