EXPERIMENTAL STUDY OF THE OYSTER GILL 



tbe rate of discharge, V, in cm^ per second is 



T7 ttD^S 



13 



(3) 



For accurate measurement of tlie velocity of the current in the tube (t) the qual- 

 ity of the carmine suspension is of great importance. The suspension must be very 

 fine and should contain no particles that may settle inside the tube; it must have the 

 same specific gravity as that of the sea water in which the oyster is kept, and its color 

 must be sufficiently deep to be noticeable when a small amount of the suspension is 

 allowed to enter the tube and forms a cone. 



To make up a suspension that will conform with these requirements the follow- 

 ing procedure should be followed: The carmine powder is ground in a glass mortar 

 with a few drops of sea water; after a very fine paste is formed more sea water is added 

 and the suspension is poured into a glass bottle, is well shaken, and is allowed to stand 

 undisturbed for five minutes. Then the upper half of it is poured into another bottle, 

 to be used in the experiments. Only fresh suspension should be used, because after 

 24 hours the carmine particles settle more quickly and have a tendency to form lumps. 



In a study of the effect of temperature and other external factors on the function 

 of the gills the carmine method has several advantages over the tank method. First, 

 no error is introduced by the possible fluctuations in the levels of v.-ater in the two 

 vessels; second, the water in the traj^ where the oysters are kept can be changed 

 easily without disturbing the animals; and third, the measurement of the rate of 

 flow can be made in a few seconds instead of several minutes, as is requii'ed by the 

 tank method. It is interesting, however, to show how the two methods check each 

 other. The following figures were obtained with an oyster that was placed first in 

 a tank, where the rate of flow of water through its gills was measured; then it was 

 transferred to a tray and after 30 minutes of rest the rate of flow of water was measured 

 again. In both cases 10 readings were made and the arithmetic mean was computed. 

 The results of this test are shown in the following table: 



Table 2. — Rale of floio of ivater determined by "tank" and "carmine" methods 



It has been found that in all cases where such a comparison was made that the 

 figures obtained by the tank method are a little lower than those obtained with the 

 carmine method. This is due probably to the additional resistance in the tube (6) 

 connecting the two vessels. It is obvious that the rate of flow can be measured more 

 accurately by employing the carmine method, while the tank method makes it possible 

 to measure the hydrostatic pressure in the gills and to collect the water after it has 

 passed by the gills. 



In the experimental study of the effect of one of the external factors on the 

 biological reaction, particular care should be exercised in eliminating the influence 



