208 
BULLETIN OF THE BUREAU OF FISHERIES 
Bleed water retards the growth of Nitzschia, the inhibiting effect being pronounced 
in concentrations of 10 percent and higher. The retardation of growth is directly 
proportional to the concentration (fig. 20). 
The experimental evidence presented in the report shows that the discharge of 
oil into the sea produces profound changes in the normal environment of the oyster. 
The substances which gradually dissolve from oil in the sea water irritate the delicate 
ciliated mechanism. In a very dilute solution they may act as stimulants, but in 
higher concentrations they inhibit the activity of the ciliated epithelium and may 
bring about complete stoppage of the current of water through the gills. The same 
substances which reduce the rate of feeding of the organism affect its food supply by 
retarding the rate of propagation of diatoms. Obviously the presence of oil creates 
adverse conditions. 
In the light of the present investigation, it is easy to conceive that when the con- 
stitution of the organism is weakened by unfavorable meteorological conditions, 
natural changes in the environment or attacks of enemies, the pollution of water with 
oil may become a deciding factor which may cause irreparable injury and death of the 
oyster. It is obvious that from the point of view of conservation, the natural oyster 
resources of the sea must be protected from tliis danger. 
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