EFFECT OF WATER-GAS TAR ON OYSTERS. 205 
opened and carefully examined. They were found to be normal in color, odor, heartbeat, 
responsiveness of the mantle, ciliary movement, and in short in every respect. 
This experiment distinctly indicates that water-gas tar in considerable doses is 
harmless to an oyster in running sea water. The conditions of this experiment more 
closely resemble those of the native habitat of the oyster than do those of the preceding 
experiment, because tides and other currents over oyster beds maintain a constant 
movement and a continuous changing of the surrounding medium. 
Experiment j. — A medium-sized oyster was injected with i c. c. of water-gas tar, 
which was distributed all around the mantle. It was then put into about 1,500 c. c. 
of sea water and carefully observed. During the next five hours it did not visibly open 
and no tar escaped from it. On the following day, however, a few drops of tar were 
floating on the surface of the water. During the next two days the oyster was only 
infrequently observed and was not seen open, but on the third day it was found nor- 
mally opened and able to close when stimulated. It was left in the same sea water 
during the next two weeks. It had then developed the usual symptoms of imperfect 
closure and when opened did not show a normally beating heart or a responsive mantle. 
This experiment confirms the first one of this series. 
EFFECT OF WATER-GAS TAR ON THE DISSOLVED OXYGEN OF SEA WATER. 
It seemed possible that tar and similar substances might in a measure reduce the 
oxygen content of water so as to affect shellfish. Mixtures of tar and sea water were, 
therefore, allowed to stand for varying periods of time and then tested by Winkler’s 
titration method to measure the quantity of dissolved oxygen in the water. The 
experiments are summarized in the following table. Three liters of sea water were used 
in each case. 
Amount of 
water-gas 
tar used. 
Time mixture 
was allowed to 
stand at room 
temperature. 
Oxygen re- 
maining in 
water at end 
of the time. 
Ctcbic 
centimeters. 
Hours. 
Parts per 
million. 
200 
20 
6- 61 
200 
24 
6. 10 
200 
45 
. 00 
200 
130 
. 08 
50 
40 
2. 71 
so 
45 
j. 10 
50 
130 
. 08 
None. 
40 
® 7. 10 
None. 
45 
8. 09 
None. 
130 
a 8. 26 
Control, sea water alone. 
These experiments show that the tar can cause the disappearance of dissolved 
oxygen in sea water. How potent a factor this may be in causing the effects of the 
tar on oysters in stagnant water it is not, however, safe to say. Oysters, as the author 
has shown, are remarkably resistant to lack of oxygen and do not when deprived of it 
60289° — Bull. 32 — 14 14 
