placed on frame D. The length of the hook is 

 adjusted by turning the nut (c). The two pans 

 of the balance are placed in a zero position, and 

 the desired weight is put on the right pan. The 

 right valve of the oj'ster is connected to the 

 writing lever (L) of the kymograph (K). The 

 writing pen (M) is attached to a signal magnet 

 which is activated by an electric timer (R) and 

 transformer (T). The timer is made by mounting 

 a plastic disc on the axis of a Telechron motor 

 making one revolution every hour. A short piece 

 of copper wire at the periphery of the disc, indi- 

 cated in figure 159 by the arrows, completes the 

 circuit every 30 minutes (at the vertical position 

 of the arrow). The weight of the balance is 

 sufficient to keep the platform from floating when 

 it is placed under water. Sea water is supplied 

 through the intake (F); the overflow (H) controls 

 the water level. This setup was successfully used 

 in a large number of tests made both in the air 

 and under water. 



Occasionally the bond between the cement cup 

 and the surface of the shell was insufficient for a 

 pull of 8 to 10 kg. and had to be adjusted by using 

 a stronger mixture and slightly roughening tlie 

 surface of the valve. In the majority of cases the 

 connection between the valve and the cement cap 

 remained intact even when the pulling force of 

 about 10 kg. was applied and occasionally the 

 muscle itself was torn in the middle. 



The purpose of the test was twofold: to study 

 the behavior of the adductor under variable 

 pulling force and to determine the time required 

 to cause the loss of tonus by the muscles that were 

 being stretched by weights varying from 2 to 10 

 kg. directly over the muscle scar. 



New England oysters kept in the harbor near 

 the laboratory were used in all the tests. The 

 oysters were about 5 inches in height and ap- 

 peared to be in good condition with the shells 

 undamaged by boring sponge. 



TESTS MADE IN AIR AND IN WATER 



Adult oysters exposed to air at room tempera- 

 ture are able to withstand the pulling force of 

 several kilograms for several days. Under the 

 weight of 7 to 8 kg. the adductor muscle opened 

 immediately (fig. 160). A force of 8 kg. (2,185.8 

 g./cm.^ of cross-sectional area of the adductor) 

 caused immediate stretching of the adductor to 

 about one-third of the maximum gaping distance, 

 which was attained within 6.5 hom's. During the 



5 hours following the initial stretching there was 

 no shell movement but the adductor retained its 

 tonus level; the response to pricking (several 

 small upward strokes on the record) M^as very 

 slight. Final stretching to 1.5 cm. gaping dis- 

 tance of the valves was relatively rapid. At this 

 stage the adductor lost the tonus and failed to 

 respond to stimulation. Upon removal of the 

 weights the muscle regained its elasticity and 

 contracted (right side of fig. 160). For several 

 hours an oyster weighing only 18.2 g., exclusive 

 of shell, was capable of maintaining a constant 

 tonus level against the pull of 8 kg. 



In all tests in which the pulling force of 10 kg. 

 per oyster was applied (from 2.5 to 3.0 kg./cm.^ 

 of the muscle area) the muscle stretched im- 

 mediately and the gape of the valves reached the 

 maximum width of 15 to 18 mm. The muscle 

 failed to respond to pricking or to the application 

 of 0.1 A" hydrocholoric acid but retained a certain 

 degree of elasticity and was able to counteract 

 the pulling force of the ligament. As soon as the 

 muscle was cut off the valves opened several 

 millimeters beyond their former position. 



Individual variations in the time recjuired for a 

 muscle to reach maximum stretching are consider- 

 able. The time needed to produce tonus loss is 

 inversely related to the weight applied to the 

 valves. The pulling force of 0.5 kg. (131 to 136 

 g./cm.^) applied for 15 days had no effect on the 

 opening of the oyster shell in the air (at room 

 temperature of 15° to 18° C). At the pulHng 

 force of about 500 g./cm.- the loss of tonus and 

 failure to respond to stimulus developed in 300 



8 Kg 

 applied 



Figure 160. — Record of shell movement of C. virginica 

 kept in air under the pulling force of 8 kg. (2185.8 g./cm.^ 

 of cross-sectional area of the adductor muscle). Arrows 

 indicate time when the weight was applied (upper left) 

 and removed (lower right). Temperature 18° to 23° C. 

 Total weight of oyster meat 18.2 g.; of shell 166 g. 

 Maximum gap (right end of the curve) 1.5 cm. The 

 distortion of the lowermost position of the lever with 

 reference to the horizontal axis is marked by the heavy 

 arrow. Time interval: 0.5 hour. 



THE ADDUCTOR MUSCLE 



177 



