EFFECT OF CRUDE OIL POLLUTION ON OYSTERS 
173 
equilibrium. A constant level is maintained in the large chamber ( Ch ) by means of 
an overflow which is so adjusted that the water content of the chamber after the 
oyster is placed in it will be approximately 1 1. Before beginning an experiment 
the stopcock ( A ) supplying sea water is turned on and the levels are carefully checked. 
After the equilibrium has been established a single drop added to the small chamber 
immediately overflows through the tube ( E ). The oyster, prepared in the same 
manner as for the cone method, is then placed in the large chamber; and the rubber 
tubing introduced in the exhalent chamber of its gills is connected to the small 
horizontal glass tube. Water pumped by the gills will immediately overflow through 
tube ( E ). An electric stirrer and thermometer are kept in the large chamber. 
3. Recording apparatus. Two platinum contact wires sealed in the glass tubing 
(P) are placed under the overflow tube ( E ) so that each drop makes a contact which 
activates a small signal magnet registering on the smoked revolving drum of a spring 
kymograph ( K ). Current for operating the magnet is supplied by a 45-volt radio 
B battery. An electric clock (T) operates another signal magnet which records on 
the drum time intervals of 1 second. Into this circuit is connected a key switch 
(5) and a 2-volt dry cell to mark the time of changing from laboratory supply to 
test solution and vice versa. Another switch ((S'!) disconnects the circuit in the 
drop counter when the kymograph is not in operation. The kymograph was set to 
make 1 revolution in 5 minutes. 
Since the pumping activity of the oyster transfers liquid (sea water or test 
solution as the case may be) from the large chamber to the smaller, it is necessary 
to have a continuous flow into the large chamber to maintain the level, otherwise 
additional work will have to be done by the gill cilia in raising water from the large 
chamber into the smaller. The change from sea water to test solution therefore is 
made instantaneously by a twist of the three-way stopcock (A). As soon as the 
shift is made the oyster is subjected to a gradually increasing proportion of test 
solution. This solution was allowed to flow into the experimental chamber for 5, 
10, or 15 minutes as noted in the tables under the heading “Duration of test solution.” 
At the rate of 200 cc per minute, from 12 to 15 minutes were required to change 
the liquid completely in the experimental chamber, so that the oyster was rarely if 
ever subjected to the full concentration of test solution shown in the tables under the 
heading “Percent soluble fraction or bleed water.” The percentage given in this 
column represents the concentration of the test solution, not the percentage to which 
the oyster was subjected. In experiment 55, table 17, for example, it should be 
understood that the figures do not show the effect of 10-percent bleed water remain- 
ing on the oyster for 10 minutes. It does show the effect of gradually replacing 
sea water with a 10-percent brine solution, the maximum concentration reached being 
unknown, but somewhat less than 10 percent. The same remarks apply to drop- 
counting experiments in which water soluble fraction of crude oil was used instead of 
bleed water. 
In the experiments using the cone method the specific gravity of the test solution 
was brought, as nearly as possible, within ±0.0002 of the laboratory supply sea water 
at the time of the experiment. This was not practicable when using the drop-counting 
apparatus, but in all cases the difference in specific gravity between the laboratory sea 
water and the test solution was kept as low as possible. Specific gravity determina- 
tions were made by Ivnudsen hydrometers certified by the National Bureau of Stand- 
ards. Hydrogen-ion concentration was checked with a Hellige-Klett color disk. 
143870—35 5 
