EFFECTS OF PULP MILL POLLUTION ON OYSTERS 
147 
SENSORY REACTION TO LIQUOR 
Along the edges of the mantle of the oyster are two rows of delicate tentacles 
which are sensory in function, and presumably serve to test the character of the 
entering water. When certain chemical solutions are brought into contact with these 
tentacles they retract sharply; and, if the chemical be sufficiently irritating, the 
retraction spreads to adjacent portions of the mantle and finally to the entire organ. 
Following such stimulation the adductor muscle contracts, protecting the oyster by 
closing the valves. 
A method of measuring the sensitivity of the tentacles was devised. It need 
not be described fully here, but it consisted in measuring the length of time, or latent 
period, after the solution touches the tentacles, that they retract. These measure- 
ments were made over a relatively small temperature range, from 16° to 18° C. 
Two series of tests with different specimens are presented in Figure 31. Each point 
represents an average of at least 10 readings. On the same graph the pH values of the 
liquor solutions are plotted. The sea water in which the specimens were immersed 
was of pH 7.8. 
The resulting latent period curves are typically logarithmic, but need no analysis 
here. The latent period is extremely short for a concentration of 8 parts per thousand, 
where the curves appear to be almost horizontal. Between this concentration and 
the minimum which produced a very sharp reaction (1 part per thousand), the curve 
increases the angle it makes with the horizontal until it becomes almost vertical. The 
measurable latent period of the tentacular reaction is limited to concentrations of 1 
part per thousand or higher. Control tests with liquor neutralized with NaOH gave 
the same latent period values, though the reaction was less clearly defined and the 
error therefore greater. 
It is interesting to compare these curves with those presented in the accompany- 
ing report by Galtsoff on the influence of liquor on the rate at which the oyster takes 
66424 — 31 4 
