14 



BULLETIN OF THE BUREAU OF FISHERIES 



of other variables that may affect the function of the organism. Gray (1922, 1924, 

 1924a) has shown that not only temperature but changes in the hydrogen-ion con- 

 centration, oxygen and carbon dioxide contents, and concentration of various salts 

 ui sea water affect the ciliary activity. In the present experiments the salinity of 

 the water, its oxygen content and the pH value were kept constant. There are 

 two factors, however, the control of which presented certain difficulties and which 

 may be responsible for considerable fluctuation in the experimental data. In some of 

 the oysters, especially in those that had been exposed for a long time to a low tempera- 

 ture, the gills were covered with a thick layer of mucus, which blocked a free passage 

 of water through the pores. These oysters exhibited wide and hregular fluctuations 

 in the velocity of the current, but after the outside and the inside of the branchial 

 chambers were washed out with sea water the current became steady. 



Mechanical stimulation represents another factor that may affect the velocity 

 of the current. Whenever the oyster attached to the apparatus was disturbed, it 

 invariably showed a change in the rate of flow, frequently stopping the current 

 entirely but coming back to normahty in a few minutes. The following record 

 of one of the experiments illustrates this fact very clearly. 



Table 3. — Effect of mechanical stimulation on the velocity of the current. — Experiment 6S, 



August 10, 1926 



It is very probable that these fluctuations are due to the contraction of the 

 branchial chambers, caused by mechanical stimulus. In the experiments described 

 below the precaution was taken to avoid mechanical stimulation, and in case the 

 oyster was disturbed by accident it was left for 10 minutes before the next readings 

 were made. 



The temperature of the water was changed by using either an electric hot-point 

 immersion heater or a battery of jars filled with a freezing mixture. The water in 

 the tray was agitated by an electric stirrer (fig. 3 s) and aerated. If necessary, the 

 tray was placed in a water jacket with a mixture of salt and crushed ice packed 

 between the walls. Readings were made after the oyster had been left for 15 minutes 

 at a given temperature. The temperature was maintained constant within 0.5° C 

 At every given temperature from 10 to 20 readings were made, from which the arith- 

 metical mean was computed. All temperature readings, unless otherwise indicated, 

 were made in centigrade. 



