48 U. S. BUREAU OF FISHERIES 
ments, in which 59 oysters were tested, showed a depression of ciliary 
activity in concentrations greater than 2.5 parts per thousand within 
30 minutes after treatment was started. Concentrations below this 
were indefinite even after 24 hours of exposure. Full recovery of the 
cilary activity did not return after treatment with 5 or 10 parts per 
thousand for 30 minutes. 
Similar results were obtained by measuring the depression of ciliary 
activity by the drop-counting technique. Depression occurred in 
strengths greater than 2.5 parts of effluent per thousand parts of sea 
water. ; 
Dr. Galtsoff’s constant-level tank combined with the rubber apron 
method of Nelson (1935) was used for automatic simultaneous re- 
cording, of the water output of experimental oysters subjected to 
pulp-mill effluent. Measurement of water filtration was made on 18 
individuals, of which 7 were controls kept in unpolluted sea water 
and 11 were treated with various dilutions of pulp-mill effluent. 
Three oysters were treated with 5 parts per thousand of the effluent, 
2 with 2.5 parts per thousand, and 5 with 1 part per thousand. Con- 
centrations of 5 and 2.5 parts per thousand gave immediate and 
marked effects. The water output was depressed so that one oyster 
filtering 14.5 liters per hour for 2 days before treatment filtered 
1 liter per hour during treatment with a solution of 5 parts per 
thousand. No recovery was evident the day after the treatment was 
stopped. Five oysters were treated with 1 part per thousand of 
pulp-mill effluent. Four out of the five responded with an altered 
behavior of muscle activity. Their water output was depressed 
within a week after treatment was started, e. g., the water output of 
one oyster was depressed 44 percent after 5 days of treatment, 
another 71 percent after 4 days. The controls remained unchanged 
in their rate of pumping. 
It is important to note that under certain conditions of experiments 
in which the rate of filtration of water was reduced or stopped the 
shell of the oyster remained open and the sheli closures were irregu- 
lar. From this it would seem that the fact that the shell of the 
oyster is open and the adductor muscle shows activity does not neces- 
sarily indicate that the oyster is feeding. 
Current measurements in the York River were carried on during 
the last few months of the year with the view of obtaining data 
which will allow calculation of the dilution of the pulp-mill effluent 
in the river. This activity will allow correlation of the laboratory 
findings with observations of conditions existing in the river. 
All the evidence so far gathered indicates the existence in the 
upper part of the river of an environment decidedly harmful to 
oysters. Studies of the cycles of temperature, salinity, and plankton 
failed to demonstrate the existence of abnormal conditions which 
may be responsible for the pathological state of the oysters. On the 
contrary, the food supply in York River appears to be more abun- 
dant than in the Piankatank. On the other hand, direct evidence of 
the harmful effect of the pulp mill effluent is provided by the physio- 
logical experiments which prove the toxicity of the black liquor. 
Its deleterious action is manifested by its effect on the adductor 
muscle and on the complex pumping mechanism of the oyster. By 
decreasing the number of hours the oyster stays open the presence 
