passage is recorded by using- a stop watcli gradu- 

 ated to one-tenth of a second. 



Glass tubing of sufficiently wide diameter should 

 be used to avoid turbulent flow. For large C. 

 virginica tubing of 5 to 6 mm. in diameter was 

 satisfactory. 



The efficiency of the lateral cilia can be ex- 

 pressed either in terms of the velocity of the cloacal 

 current or by computing the mechanical work 

 they perform. The fact that a distinct cone forms 

 at the center of the tube through which the current 

 is running indicates that we are dealing with a 

 viscous flow for which the velocity can be ex- 

 pressed by the Poisseul's formula: 



S-- 



D-Ap 



In this formula S is the velocity at the axis of the 

 tube in cm. /sec; D is the diameter; and / the 

 length of the tube in cm.; A p is pressure drop 

 between the two marks along the tube in dynes/ 

 cm.'; and n is viscosity of sea water in poises 

 (C.G.S. unit). 



The mean velocity (Sm) of the current of the 

 entire cross sectional area of the tube is one-half 

 the velocity at the axis. The rate of discliarge, 

 V, in cc. per second is computed by using the 

 following formula: 



V- 



ttD'O.BS 



The rate of mechanical work 11' (in ergs per 

 second) can be determined from the formula: 

 W=2irlixS^. For a detailed discussion of the 

 mechanical activity of oyster gills, the reader is 

 referred to the original publication of Galtsoff 

 (192Sb). 



The cone method is simple and requires no 

 elaborate eciuipment. It can be used in any field 

 or temporary laboratory and is particularly use- 

 ful for rapid toxicity tests in tracing the phys- 

 iologically active components of various pol- 

 lutants. The method has, however, several 

 limitations that should be kept in mind. First, 

 the volume of water passing through the cloaca 

 does not represent the total amount transported 

 by the gills because a certain portion of the water 

 is discharged tln-ough the promyal chamber. 

 Second, the tests should be completed ui 1 day because 

 the prolonged presence of tubing inside the cloaca 

 and of the wedge between tlie valves may produce 

 pathological conditions. Because of the sensi- 



tivity of the cilia to mechanical disturbance great 

 care should be exercised to avoid jarring, shaking, 

 and vibrating when preparing a test. The oj'sters 

 usually recover within 12 hours after being placed 

 in running sea water and show no ill eft'ects of the 

 narcosis and handling. 



EFFECT OF TEMPERATURE 



The cone method proved satisfactory in a study 

 of the effect of temperature on the efficiency of the 

 lateral cilia. Tlie results of many tests performed 

 in the Woods Hole laboratory show considerable 

 variability in the velocity of the cloacal current 

 of oysters of the same size and origin. At a given 

 temperature and under identical conditions the 

 lateral cilia of some oysters work faster than those 

 of others. Consequently, no definite rate of work 

 maintained by the gill epitiielium at a specified 

 temperature might be considered as typical or 

 normal for an oyster of a stated size and type. 



An example of the effect of temperature on cur- 

 rent velocity produced by the lateral cilia of oysters 

 of identical size transporting water at different 

 rates is shown in figure 140. In both experiments 

 the water was agitated by an electric stu'rer and 

 its temperature was changed by using heating or 

 cooling units placed at the end of the tank far- 

 thest from the oyster. Not less than 15 minutes 

 for adjustment was allowed at each temperatui-e 

 step. Readings were made starting at 20° C. and 

 decreasing to the extreme low temperature at 

 which no cm-rent was produced. Then the water 



Figure 140. — Effect of temperature on the velocity of 

 the cloacal current produced by slow (lower curve) and 

 fast (upper curve) adult oyster, C. viiginica, of about 4 

 inches in height. Each dot represents the mean 

 velocity of the current of 10 consecutive readings made 

 at intervals of 2 to 3 minutes. Carmine cone method. 



THE GILLS 



145 



