EFFECT OF WATER-GAS TAR ON OYSTERS. 
203 
time it was cleaned and dried and found to weigh 71.6 grams. It had formed new shell 
all around the edge. Opened it gave no smell of tar, the heart was beating and the 
mantle was normally sensitive to mechanical stimuli. Part of the heart and portions 
of the gills were discolored. 
Control experiment . — An oyster weighing 72.4 grams was put in a battery jar with 
2,500 c. c. of sea water. The water was changed during the next 10 days as in the pre- 
ceding experiment and was then left stagnant during 8 weeks. Examination then 
showed no noticeable new shell, but the heart, gills, and mantle were quite normal. 
The experiments of this series indicate that when considerable quantities of 
water-gas tar are in intimate contact with oysters in stagnant water serious or fatal 
effects are produced. Under these circumstances the oyster can not use its natural 
defense against a relatively or entirely insoluble substance. When the water is stag- 
nant, there is little opportunity to eject such substances and free the organism from 
them. As will be shown later, the oyster can rid itself of water-gas tar when in running 
sea water. When the tar can not be ejected it seems to produce an effect similar to 
paralysis, so that the initial symptom is a failure of the adductor muscle to respond 
to stimulation of the sensory nerves. No conclusions as to the structures specifically 
affected can be drawn from these experiments. Whether the fatal effects produced in 
five of the above experiments were due to a direct toxic effect of water-gas tar, or to 
some indirect effect also, does not appear from these experiments. 
SERIES II. 
Method . — Two oysters were put in each of four battery jars. Each jar was arranged 
with two siphons, one bringing sea water from an aquarium to the jar with the lower 
end of the siphon about 2 inches below the level of water maintained by the other siphon, 
which carried water from the jar to a sink. The running water therefore tended to 
carry off the light floating oils but left the heavier tar sticking to the bottom and sides 
of the jar. The siphons were so arranged that each jar contained constantly about 
2,500 c. c. of sea water. Into each jar there were put 30 c. c. of water-gas tar mixed 
with sand and thoroughly smeared over the bottom and sides of the jar and on the 
shells of the two oysters. From time to time during the following weeks small amounts 
of tar were added to replace that carried away by the siphons. After remaining in 
the jars as described during nine weeks the oysters were cleaned, weighed, and examined. 
Comparison of their weights at the beginning and at the end of the experiments is given 
in tabular form ; 
Jar. 
Initial 
weight. 
Final 
weight. 
Grams. 
Grams. 
1 98.0 
99-0 
\ 47-8 
47.8 
/ 92- 0 
92. 0 
\ 52. 4 
52.3 
/ 96.8 
94.0 
\ 61.8 
62. 5 
f 101. I 
100. 7 
\ 45 - 2 
44*3 
