SENSORY STIMULATION OF THE OYSTER, OSTREA VIRGINICA, BY CHEMICALS 257 
The question arises as to whether the reactions are due to stimulation of different 
sensory endings the thresholds of which are different. Or possibly different receptors 
are stimulated separately; one, for example, by the anions, another by cations, and 
still another by undissociated molecules. This is a problem which may be solved, 
and further experiments are under way for this purpose. 
What appears possible is that there is a measurable refractory period of the ten- 
tacular muscle fibers and that following initial stimulation contractions follow at 
regular intervals. Stimulation results first in retraction of the tentacles involved and 
then, after a considerably longer latent period, the adductor muscle contracts, closing 
the valves. In Figures 10 and 11 the results of a series of tests are given to show the 
relationship existing between the initial response of the tentacles and the following 
reaction of the adductor muscle. It is not practicable to employ the response of the 
O 0.5 1.0 1.5 2.0 
CONC.(M) 
Figure 10. — Average latent period values for the tentacu- 
lar (open circles) and adductor muscle (solid points) 
reaction to a series of concentrations of sodium chloride. 
(See also fig. 11) 
Figure 11.— Logarithmic expression of data given in Figure 
10 for responses of tentacles and adductor muscle to sodium 
chloride 
adductor muscle in this work, for after the oyster has been stimulated a few times the 
shells close and remain so for a considerable period. 
Certain experiments with mixtures of substances are of interest with regard to 
this phase of the subject. Cumarin (0.0009 per cent) produced a reaction following 
8.4 seconds; and the latent period for quinine (0.0007 per cent) was 9.2 seconds. 
A mixture containing both 0.0009 per cent cumarin and 0.0007 per cent quinine gave 
a latent period value exactly the same as that of cumarin alone, 8.4 seconds; thaf is, 
the latent period measured was that of the substance (cumarin) in the mixture which 
alone would produce the shorter reaction time. In another experiment the latent 
period for cumarin (0.0013 per cent) was 6.05 seconds, and that for quinine (0.001 
per cent) was 5.85 seconds. The solution consisting of both 0.0013 per cent cumarin 
and 0.001 per cent quinine gave a latent period, within a small error, the same as that 
