182 
BULLETIN OF THE BUREAU OF FISHERIES 
In experiments 143 and 177 of this group we find, for the first time, the pumping 
immediately stopped on addition of the soluble fraction, and not beginning again 
until the test solution was replaced with fresh sea water. As in previous experi- 
ments, an extreme effect is probably attributable to poor condition of the oysters, 
for the difference between the specific gravities of the laboratory sea water and the 
soluble fraction was very small, 0.0001 in experiment 143 and 0.0003 in experiment 
177. Nor can the stoppage of flow be attributed either to an increase in specific 
gravity of the sea water after washing with oil, or to the number of times the oil 
was washed. 
The least effect of 80-percent solution occurred in experiment 165, in which the 
reduction in flow amounted to 59.1 percent. This relatively small effect is doubtless 
also due to the condition of the oyster, no. 165, being for some reason better able to 
withstand the test solution than any of the others in the group. 
Eight experiments were made with 100-percent soluble fraction (table 11, 
fig. 7). The average tem- 
perature of the laboratory 
sea water for all experi- 
ments was 27.3° C. The 
specific gravity was high, 
1.0272 to 1.0277, except in 
the last experiment, where 
it was 1.0230. 
The average reduction 
in ciliary activity amounted 
to 87.6 percent. In five ex- 
periments there was a com- 
plete cessation of pumping. 
The results of all the 
experiments with the cone 
method show, without any 
doubt, that the presence of 
the water-soluble fraction 
of crude oil exerts an inhib- 
iting effect on the efficiency 
of the ciliary motion of the 
gill epithelium, the work of 
which is interfered with in such a way that less water is pumped through the gills, and 
consequently the rate of feeding of an oyster is decreased. The decrease in efficiency 
of the epithelium is directly proportional to the increase in concentration of the 
soluble fraction. This is clearly seen from an examination of figure 8, which shows 
the percentage of depression caused by various concentrations. The values plotted 
in the figure are the averages, recalculated from the data given in table 11, based on 
the efficiency of the ciliary motion in the controls as 100 percent. 
A relatively high degree of depression caused by the 20-percent solution may be 
considered as a breaking point in the curve, but so small a number of observations 
is not sufficient to determine this point with certainty. Regardless of the graphical 
interpretations that can be made concerning the shape of the depression curve, one 
Figure 8.— Depression of rate of pumping of gills caused by various concentrations 
of water soluble fraction of oil. 
