SENSORY STIMULATION OF THE OYSTER, OSTREA VIRGINICA, BY CHEMICALS 259 
The table shows well the confusion given rise to by such fluctuations. Obviously 
temperature was not responsible for such behavior. It is clear that there are in this 
case two different latent period levels which appear. The reason for the change from 
one to the other is puzzling. 
The existence of two latent period levels of a different nature was shown in the 
tests with NaOH. (Figs. 8 and 9.) In this case two typical curves crossed each 
other, and it was suggested that one curve represented the response to Na ions and the 
other that to OH ions. Crozier made studies of the sensory response of earthworms 
to acids (1918a) and to alkalies (1918b). His method was to measure the time re- 
quired for withdrawal of the worm from the test solution. Certain of his logarithmic 
curves (1918b, fig. 3) show sharp breaks suggesting the existence of two intersecting 
curves. His method was not adapted to show whether each curve was continuous in 
both directions beyond the intersection. The response studied — locomotion for a 
certain distance — represents not a simple response but all of the neuromuscular 
activity involved in locomotion. 
Crozier found it necessary to subtract from the reaction time a figure representing 
“the mechanical resistance to, or disadvantage of, its method of progression,” in order 
for the effect, j, to be directly proportional to the concentration. After sub- 
traction of this factor the logarithmic curves make an angle of 45° with the y-axis. 
In the present experiments, also, it was found that a constant must be subtracted from 
the latent period values in order for the equation, C X T = K, to obtain. While in the 
case of the complicated locomotor activity of the worm it is conceivable that the 
“mechanical disadvantage” might account for this factor, it appears improbable that 
such an explanation would suffice for the comparatively simple retraction of the 
delicate tentacles of the oyster. More likely appears the hypothesis that the layer of 
mucus constantly present serves to impede the penetration of the molecules of stimu- 
lating chemical. Further experiments are under way to clear up this point. 
SUMMARY 
(1) The tentacles on the mantle of the oyster react to chemical irritation by re- 
tracting sharply. They are sensitive to odorous compounds, such as cumarin, and 
to salts, acids, alkalies, and quinine, but show no clear reaction to cane sugar. 
(2) Graphs plotted to show the relationship between concentration and latent 
period indicate that the effect, considered to be represented by the reciprocal of the 
latent period, is directly proportional to the concentration. However, in order for 
this to be the case it is necessary to subtract a constant from the latent period values. 
This constant is supposed to represent the impedence due to mucus covering the 
receptors. 
(3) In certain cases it was found that the latent period fluctuated between two 
levels. For a series of concentrations the values obtained would fall into two well- 
separated and distinct curves, mathematically comparable. This does not appear 
to be due to fatigue or to variations in temperature. 
(4) The latent period values for solutions of sodium hydroxide in sea water appear 
to be most clearly represented by two intersecting curves. Expressed logarithmically 
one of these makes an angle of less than 45° with the horizontal and may indicate the 
response to sodium cations; the angle of the other is approximately 45° and may 
