168 
BULLETIN OF THE BUREAU OF FISHERIES 
Sharp contraction of the adductor muscle caused by a sufficiently strong con- 
centration of an irritating substance produces a twofold effect: The oyster snaps its 
valves to expell the irritating substance from the inhalent chamber and then keeps 
the valves tightly closed to protect itself from further irritation or injury. Since 
feeding can take place only when the muscle is relaxed and the valves are open, the 
number of hours the oyster remains open determines to a certain extent the dura- 
tion of feeding. One must bear in mind that the principal organs of feeding of an 
oyster are the gills, the function of which consists of filtering large quantities of water 
and in carrying microscopic food particles toward the mouth. (For a detailed de- 
scription of the function of gills see Galtsoff, 1928.) Obviously the gills can function 
only when the valves are open. 
The presence of a toxic or irritating substance may affect the adductor muscle 
which will cause the oyster to close, therefore reducing the number of feeding hours 
and the quantity of food consumed by it, or it may have direct harmful effect on the 
delicate ciliary mechanism of the gill. In both cases the feeding of the organism is 
impaired. The effect of oil on ciliary activity of the oyster is discussed later. At 
present we are interested only in its effect on the muscular activity. 
Records were obtained of the behavior of the adductor muscle of oysters sub- 
jected to Pelto oil. Immobilized oysters were attached to 24-hour recording instru- 
ments in such manner that every shell movement was transmitted and reproduced 
graphically upon charts which were divided into hours. The number of hours of 
activity and the number of closed hours were counted for each day. 
The running water, supplied to 4-liter dishes containing 2 mounted oysters, 
flowed through a layer of oil and out from a siphon. Fifty cc of Pelto oil was used 
to form the surface layer. As the force of the inflow caused globules to be constantly 
forced down into the water, much of the oil driven into the water gradually adhered 
to the sides of the dish and to the mounted oyster. Some oil was also lost occasion- 
ally through the outflow, and fresh oil, therefore, frequently was added so that a 
heavy surface film was always maintained. The oysters were so placed in the dishes 
of running water that the upper valve was less than an inch below the surface of 
the oil. 
Table 8. — Average number of hours oysters remain open 
IN RUNNING SEA WATER UNDER OIL 
Oyster no. 
Dates 
Days 
Hours 
Temper- 
ature 
range 
Oyster no. 
Dates 
Days 
Hours 
Temper- 
ature 
range 
1933 
0 C. 
1933 
0 C. 
I3y 
12 
8.6 
23-26 
406... 
Aug. 18-25. 
7 
10.8 
25-28 
Do 
July 12-23... 
11 
12. 1 
22-25 
Do 
Aug. 25-29 
4 
8.9 
28-30 
Do 
July 23- Aug. 5 
13 
8. 5 
27-30 
Do 
Aug. 29-Sept. 9 
7 
11.0 
26-29 
Do... 
Aug. 5-12 
7 
12.2 
24-27 
Do 
Sept. 9-15. 
6 
11.6 
28-30 
13x 
June 31-July 12 
11 
10.8 
23-26 
Do 
Sept. 15-20 
5 
12.5 
25-28 
Do 
July 12-19 
7 
9.5 
22-25 
Do 
Sept. 20 -Oet. 2 
12 
8. 5 
24-27 
Do._ . 
July 19-Aug. 2 
14 
16.6 
25-28 
169. 
Aug. 8-17 
9 
8.2 
26-29 
354.. 
July 10-23..”. 
13 
7.3 
23-26 
Do 
Aug. 17-24 
7 
10.5 
24-27 
Do 
12 
9.9 
26-29 
Do 
Aug. 24-Sept. 5 
8 
11.0 
26-29 
Do 
Aug. 4-15. 
12 
8.5 
24-27 
Do 
Sept. 5-13 
8 
10.2 
24-27 
Do.. . 
Aug. 16-27 
11 
8.6 
25-28 
Do 
Aug. 18-24 
6 
10.2 
24-27 
Do 
Aug. 27-Sept. 14___ 
14 
10.3 
26-29 
Do 
Aug. 24-Sept. 7 
n 
7. 1 
26-29 
Do 
Sept. 14-261 
10 
11.5 
24-27 
Do 
Sept. 7-14. 
7 
8.3 
27-30 
150__ 
Juiy 18-24 
6 
12.4 
25-28 
Do. 
Sept. 14-29 
13 
8.2 
24-27 
Do 
Do 
Aug. 3-17 
14 
13! 1 
24-27 
7 
292 
1 10. 5 
22-30 
408 
Aug. 13-18 
5 
8.2 
26-29 
1 Average. 
