tissue. Similar differences in ratio were observed 

 during all seasons although the absolute figures 

 of oxygen consumption varied. It is probable 

 that a similar ratio may be found in oysters and 

 other bivalves. 



METHODS OF STUDY 



In the old method of determining the rate of 

 oxygen consumption, oysters were put in a small 

 container filled with sea water wliich was analyzed 

 for oxygen content at the beginning and at the end 

 of the test. The method was crude since no atten- 

 tion was paid to the increase in the concentration 

 of metabolites in the water or to the opening and 

 closing of the shells during the test period. The 

 results obtained under such conditions were 

 erratic. Some of the defects of this method were 

 eliminated by using the open-chamber technique 

 (Galtsoff and Whipple, 1931). The oyster was 

 mounted on a support and placed in an open jar 

 in sea water under a layer of paraffin oil. Shell 

 movements were recorded on a kymograph. The 

 water in the jar was gently stirred, and the volume 

 drawn off for oxygen determination was replaced 

 by fresh sea water of known oxygen content. The 

 temperature was kept constant by placing the 

 respiratory chamber in a water bath equipped 

 with proper temperature control. The sea water 

 used for the test was filtered to eliminate the effects 

 of photosynthesis and respiration of plankton. 



More reliable results were obtained by using the 

 modified respiration chamber of Keys (1930a, 

 1930b) which was designed originally for studies 

 of oxygen consumption by fishes. The method 

 was used in my laboratory to determine the 

 fluctuations in the rate of oxygen consumption by 

 oysters that were kept for several hours in slowly 

 running water of constant oxj^gen content (Galt- 

 soff, 1947). During the period of testing the shell 

 movements were recorded and the position of the 

 borders of the mantle was observed. The appa- 

 ratus (fig. 183) consists of a respiratory chamber A 

 submerged in a large water bath in which the 

 temperature is kept constant within ±0.2°C. 

 Filtered sea water of known oxygen content is 

 supplied by gravity from a battery of carboys, and 

 a uniform rate of delivery is controlled by head 

 pressure kept constant in a small delivery vessel 

 H. The water from the carboys is fed to this 

 vessel at a constant rate; and excess water is 

 voided bj' suction (on the right side of vessel H) 

 in order to maintain the constant level in H. The 

 tubing that leads from vessel H is divided at I into 



two branches of equal diameter, one leading to the 

 collecting vessel L, the other to the respiratory 

 chamber A. The constant rate of flow is main- 

 tained by means of two capillary glass tubings of 

 equal diameter O inserted in the delivery tube. 

 Stainless steel valves, pinch and glass stopcocks 

 were found unsuitable for this purpose because of 

 the slight shifting of their moving parts. Glass 

 tubings of appropriate diameter were selected for 

 each test from a set of several calibrated capil- 

 laries kept on hand, and the rate of flow of water 

 was carefully checked at the beginning and end 

 of each test. Before entering the respiratory 

 chamber A, the water passes through a glass coil 

 B (shown in figure 183 in a vertical position but 

 actually lying flat on the bottom) which is com- 

 pletely submerged in water bath C. The bath is 

 equipped with a constant temperature controller 

 (not shown in figure 183). The water leaves the 

 respiratory chamber through an outlet on the top 

 and runs to one of the collecting cylinders K; 

 by using a three-way stopcock J the flow of water 

 may be shifted from one collecting cylinder to the 

 other. The cylinders are suspended from pulleys 

 and are counterbalanced by weights N. When 

 empty the cylinders are raised above the water 

 tank M; as they are filled with water they descend 

 until they are partially submerged. Heavily 

 paraffined wooden floats prevent direct contact of 

 water collected in the cylinders with the air. For 

 taking samples the cylinder is disconnected from 

 the respiration chamber by turning off the stop- 

 cock J so that water is diverted to the second 

 cylinder. Then the closed cylinder may be lifted 

 out and the water taken through the drain cock at 

 the bottom. Glass stoppered Erlenmeyer flasks 

 of 100-ml. capacity were used for sampling. The 

 sample for analysis is taken at the middle level of 

 the cylinder between the 300- and 500-ml, marks. 

 Water which runs directly from the supply carboy 

 is sampled in the same manner. The difference 

 in the o.xygen content of the water running in and 

 out of the respiratory chamber multiplied by the 

 rate of flow through the chamber gives the quantity 

 of oxygen consumed by the oyster in a unit of 

 time. 



Each oyster was prepared carefully for the tests. 

 Shells were scrubbed with a wire brush, rinsed in 

 fresh water, dried, and covered with melted 

 paraffin applied with a small brush. During this 

 treatment the oyster was kept vertical with its 

 hinge at the bottom, and paraffin was applied in 



TRANSPORT OF WATER BY THE GILLS AND RESPIRATION 



201 



