SENSORY STIMULATION OF THE OYSTER, OSTREA VIRGINICA, BY CHEMICALS 255 
—Average latent period values for different concentrations of KOH (solid 
points) and NaOH (open circles). (See fig. 9) 
made, but the others are entirely comparable and need not be given. In Figure 8 the 
curves representing the latent period values for each concentration are entirely 
different for the two alkalies. While the latent periods for KOH fell into a curve 
typically like those described in the preceding pages, the results obtained with NaOH 
fall distinctly into two such curves (A and B, fig. 8) which cross one another at a 
concentration of about 0.07 M. 
In measuring the latent 
period of the tentacular re- 
action the time up to the 
first visible sharp reaction 
is used. It was observed in 
the early experiments with 
NaOH (fig. 8) that the lat- 
ent period for concentra- 
tions of 0.1 M. or above 
were very short, and at the 
next lower concentrations 
much longer than expected. 
There appeared to be a 
sudden break in the curve. 
When tests with various 
concentrations were repeat- 
ed it was found that one 
series would give a long reaction time and another series with the same solution 
would give a short latent period. The points appeared to fall along the lines as shown 
in the figure. It is probable that the reactions in both latent period groups occurred 
in all cases, but that at some times those of one group would be sharp enough to be 
detected while at other times the clear reactions would fall into the second group. 
For some time during the tests it was thought that the error of the method was simply 
very large, but the latent period values persisted in falling along the lines shown. 
The records obtained with KOH, 
on the other hand, were of a decid- 
edly different sort (fig. 8). So far 
as could be determined the latent 
period curve was single . The points 
fall into a curve similar to those of 
the salts. By plotting the results 
logarithmically (fig. 9), the dual 
nature of the results with NaOH 
is made even clearer. While the 
points representing the reaction to 
KOH may be considered to fall into 
a single straight line, two such lines 
are required to satisfy the values obtained with NaOH. The difference is probably 
of some significance for all of the tests were made upon a single specimen within the 
period of a few days. 
In the description of the experiments with salts it was pointed out that the 
logarithmic curves made an angle of something less than 45° with the horizontal. 
In Figure 9 it appears that the angle made by the KOH curve is only about 20°, 
