EFFECTS OF PULP MILL POLLUTION ON OYSTERS 
155 
The difference between the control and the experimental oysters is very clear, although 
all specimens are quite active, as is typical of oysters which are immersed after being 
in air for some time. 
Soon another type of shell reaction begins, namely, the tendency to close and 
remain closed for increasingly long periods. In Figure 35, a few hours farther ad- 
vanced than Figure 34, this tendency is shown. However, the initial effect, very 
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Figure 35— Reproduction of portion of kymograph sheet showing records of specimens used in experiments 
Nos. 24 and 25, a few hours later than that shown in Figure 34. The tendency to remain closed (high 
straight lines) and the rapid movements when open are well shown 
frequent closures, is still to be observed during the periods of activity or “openness.” 
This continues for some time, depending upon the concentration of liquor and the 
consequent rapidity with which the toxic action occurs. Then (fig. 36) the periods 
of remaining closed become shorter and the reactions while open less frequent. At 
the same time the adductor muscle slowly loses its power to close the shells com- 
pletely. In the figure this is more obvious in the second record than in the first. 
That the closure is incomplete after the short opening period is shown by the lower 
