Evidently a change in the number of revolutions per second of the trapped wave or the amplitude of the contractions would cause an error in the determination of the effect of 02 concentration on metabolism, and in order to estimate the limits of such errors the relative metabo lism of the muscle and other tissues was studied. The umbrellas of 3 cassiopeas, a, b, and c, of the same size (diameter =11.5 cm.) were used (each for a series of experiments). In some experiments the rhopalia remained and the normal pulsations were generated, in others a trapped wave was induced, and in others the subumbrella was removed or merely the mesoglcea left. The apparent (but slight) metabolism of the mesogkea was probably entirely due to a few remnants of epithe lium and to bacteria, which always attack the mesogkea when the epithelium is removed. At any rate, the metabolism of the meso glees is too small to be of significance. The pH was 8.2 and the per liter 4.5 c.c. at the beginning of each of the experiments.
The removal of the rhopalia in the umbrellas with trapped waves or without pulsations reduced but slightly the amount of tissue. If we take the metabolism of the normal pulsating umbrella at 100, the exumbrella is about 14 and the resting subumbrella 60, with an addition of 26 for normal pulsations or 65 for trapped wave. Therefore, the neuro-muscular tissue may perform about 26 to 46 per cent of the metabolism, and changes in rate or amplitude of the contraction-wave are to be avoided as much as possible.
In subsequent experiments, the manubrium and rhopalia were removed from the cassiopea and a C-shaped cut was made through the neuro-muscular layer, about one-third the radius from the outermargin of the umbrella, and a trapped wave was induced by stimulation near the outer margin. The wave passed around the outer part of the subumbrella, and each time it passed the opening of the C it spread to the inner part, dividing into two equal waves, meeting on the far side with mutual destruction. In this way the outer part, in which the trapped wave was first induced, was made pacemaker and the result was a more permanent wave. The wave causes circulation of water against all parts of the epithelium except a small portion of the exum brella which has a very low metabolism. If the oxygen concentration was reduced to zero, the wave stopped and metabolism ceased until oxygen was readmitted. In one experiment an umbrella was kept 7 hours at zero 02 concentration, then 3 hours with 02 and a trapped wave, and 7 hours at zero 02 concentration, during which it gave out no or other acid products affecting the pH perceptibly; 30 seconds after it was taken out of the chamber a trapped wave was started and this constantly increased in amplitude for 10 minutes, at the end of which time the amplitude was normal.
Oxygen was removed from sea-water in various ways, with the air pump and agitation, by boiling, and by allowing a cassiopea to remain in it until the pulsations ceased, as seen through a peep-hole in such a way that photosynthesis was practically avoided. In no case did
the analysis show less than about 0.05 c.c. per liter, but that amount probably entered with the KI and solutions and around the ground stopper of the analysis bottle. At any rate, we should con sider 0.05 c.c. to be within the limit of error of the method if no correc tion were made for 02 in the reagents.
The variation in metabolism after removal of the manubrium and initiation of a trapped wave is shown in table 21. The diameter of the umbrella was 11.5 cm. at the beginning of the first experiment and at the beginning of each experiment the pH was 8.2 and the 02 per liter 4.5 c.c. It is evident that the metabolic rate may vary rapidly for 3 hours after the manubrium is removed and the trapped wave is started; therefore, in the subsequent experiments the umbrella was not placed in the respiration chamber until these 3 hours had passed. The same umbrella used in the above experiments but 21 hours after the opera tion was used to determine the effect of reduced oxygen concentration. The average 02 concentration during the experiment was 1.5 c.c. per liter and the 02 used per hour 1.03 c.c., being a decline of 20 per cent in rate of oxidation, with a reduction of the oxygen-concentration to about half its original value. This and some later experiments are as shown in table 22.
These determinations show that oxidation is reduced about 20 per cent when the 02 concentration is reduced about 50 per cent; or the oxidation increases about 25 per cent when the 02 concentration is increased about 100 per cent.
The above experiments show that the rate of oxidation varies with the tension of oxygen in the sea-water constantly circulated against the surface of the epithelium in which oxidation takes place. In the total absence of oxygen no measurable quantity of CO2 or other acid products are given out, and we may infer that the metabolism is sus pended. If oxygen is readmitted after a suspension of the metabolism for 7 hours, the rate of metabolism rises apparently to the normal within 10 minutes. No anaerobic processes were detected during absence of oxygen for 7 hours, but in the absence of oxygen for 16 hours, anaerobic or hydrolytic processes take place. No evidence was found to indicate that these anaerobic processes constituted the metabolism of the cassiopea. On the contrary, a great multiplication of bacteria was associated with them, and the cassiopea was partly dissolved and could not be revived by readmission of oxygen. We may assume that oxygen protects the cassiopea from the attacks of bacteria (probably anaerobes). Since the bacteria enter from the surface, it seems prob able that the cassiopea might live indefinitely on so small a supply of oxygen that it is used in the superficial cells as fast as it diffuses into them, and none reaches the deeper cells. If this be true, the variation in oxygen consumption with variation of supply might be the expression of a variation in the number of cells receiving oxygen. In other words, this would be a diffusion phenomenon.