HOURS AFTER START 



Figure 189. — Oxygen uptake, in mg. of oxygen per oyster, 

 per hour, measured at half-hour intervals. Tempera- 

 ture 24.5° C; sahnity of water 31.9°/oo. Oyster A 

 (solid line): wet weight of tissues 16.1 g. ; dry weight 

 2.5 g. Oyster B (broken line): wet weight of tissues 

 12.5 g. ; dry weight 1.4 g. Before the tests were made 

 these 6-year-old oysters from Long Island Sound were 

 kept for 35 days in Woods Hole Harbor. August. 



Oxygen Uptake Under Continuous Pull of the 

 Adductor Muscle 



Increased shell movements of oysters are asso- 

 ciated with an increased oxygen uptake. This has 

 been reported by Galtsoff and Whipple (19.31), 

 who found that oxygen consumption by the oysters 

 wliich made only five or less shell closures per hour 

 was about 20 percent lower than that of oysters 

 which closed and opened their valves 30 times or 

 more per hour. The effect on the metabolic rate 

 of the oyster of the resistance of the adductor 

 muscle to a continuous pull and of the mainte- 

 nance of a forced muscle tonus has been studied 

 for large New England oysters using the equipment 

 designed to determine the power of the adductor 

 muscle (see: p. 176, ch. VIII). The entire plat- 

 form upon which the oyster was mounted was 

 lowered into a tank of 3 1. capacity filled with 

 filtered sea water and covered by a layer of light 

 mineral oil about 0.5 inch thick. The water was 

 stirred gently, and the temperature was kept con- 

 stant at 24° ±0.3° C. Samples of water, of 100- 

 ml. capacity, withdrawn from the tank were 

 immediately replaced by an equivalent volume of 

 filtered sea water of known oxygen tension. An 

 accurate record was kept of tiie total volume of 

 water in the tank, and its oxj'gen content was re- 

 computed after every addition. During the tests, 

 which lasted from 3 to 6 hours, sampling was made 

 every 30 miimtes. The initial oxygen tension 



varied in different experiments from 4 to 5 ml. 

 per 1. As the muscle was stretched by the pulling 

 force of 4 kg. (fig. 191), the oxygen uptake, which 

 ordinarily was 3.7 to 5.0 mg. per hour per oyster, 

 decreased to 2.2 mg. Similar results were ob- 

 tained in several tests in which the pulling force 

 varied from 2 to 4 kg. per oyster. In all cases the 

 adductor muscle was stretched but continued to 

 maintain tonus at a new level. In many instances 

 the up and down shell movements persisted but 

 on a noticeably reduced scale. In the majority of 

 cases the oxygen uptake decreased markedly to 

 almost zero as the shell movements were reduced. 

 During the test shown in figure 192 the shell move- 

 ments were limited and their character did not 

 change after the pulling force of 2 kg. was applied. 

 The new tonus level was accompanied by an im- 

 mediate decrease in the uptake of o.xygen to about 

 one-half its preceding rate. In 2 hours the con- 

 sumption of oxygen almost stopped. 



In several instances a sudden increase in oxygen 

 consumption was observed when the oj'ster was in 

 the respiratory chamber despite a pulling force of 

 2 kg. (fig. 193). Examination of the water re- 

 vealed the presence of eggs or sperm released from 

 the gonad. The metabolic rate of the sex cells 

 contained in the gonads was suddenly increased as 

 soon as the cells were free in water. Within the 

 gonad tubules the sex cells are tightly packed and 



AFTER START 



Figure 190. — Oxygen uptake, in mg. of oxygen per oyster 

 per hour, measured at half hour intervals. Temperature 

 24.5° C: salinity of water 31.8°/c,o. Oyster A (solid 

 line): wet weight of tissues 15.2 g. ; dry weight 2.1 g. 

 Oyster B (broken line): wet weight of tissues 12.8 g. ; 

 dry weight 1.5 g. Before the test these 6-year-old 

 Long Island Sound oysters were kept for 30 days in 

 Woods Hole Harbor. August. 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



209 



