On Changes in the Sea and Their Relation to Organisms. 239 



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 titrations, 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 O2 tension is ^'ery 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. €., resting on a glass plate, with the exumbrella in 

 contact with the glass (and the average of 2 diame- Table 15. 

 ters at right angles to one another taken). Some 

 rough preliminary determinations showed the O2 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 O2 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. = 2.25^ 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 O2 per liter at the beginning of the ex- 

 periment are given; the pH was about 0.09, while the O2 was 1.5 c.c. 

 lower at the end of each experiment. The average O2 during each 

 experiment influences the O2 used per hour, but apparently no difference 

 in the quotient of the O2 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 



