252 
BULLETIN OF THE BUREAU OF FISHERIES 
POTASSIUM CHLORIDE 
Latent period studies were made with a number of inorganic salts, but at this 
place data need be given for only KC1, NaCl, and MgCl 2 . 
A typical record is that shown in Figure 2 for potassium chloride. The latent 
period values all fell within 2.5 
seconds, but the curve is neverthe- 
less very similar to that just de- 
scribed. It was possible to measure 
the reaction time for concentrations 
as low as 0.01 M., but solutions of 
0. 2 M. or higher caused such violent 
contractions of the whole mantle 
that the difficulties of experimen- 
tation were great. 
The logarithmic curve (fig. 2) 
is similar to that shown in Figure 
1, except that the angle made with 
the horizontal axis is less. Typical 
of nearly all of the records for salts 
is an angle of less than 45° for the 
logarithmic curve. It is assumed 
that this is due to some factor, such 
as diffusion, which causes the latent 
periods to be longer than expected. That is, the relationship, CxT = K, must be 
modified to C X (T — X) == K. The significance of the factor, X, will be discussed later. 
SODIUM CHLORIDE 
In Figures 3 and 4 the results of two series of tests with solutions of NaCl are 
given. The series were made with different specimens at different times, and the 
latent period values of series 1 are consistently higher than those of series 2. This 
difference probably was not due to temperature for that was approximately the same 
in both cases. It may have been due to difference in light intensity, for according to 
Kribs (1910) bright light sensitizes the chemical receptors of Aelosoma. It was 
possible to measure the reaction time at concentrations only as low as 0.1 M., which 
is very high as compared to the threshold for KC1. It is well known, however, that 
the potassium ion is very highly stimulating to many organisms (Hopkins, 1932). 
In Figure 4 the two curves are presented in logarithmic form. The curves are 
drawn through the points as parallel lines, though this need not necessarily be the case. 
The angle of the curves is less than 45°, as in the case of KC1, and all other salts. 
MAGNESIUM CHLORIDE 
It has been a source of confusion in this work that in certain experiments the 
latent period seemed to change almost suddenly from short to long. For example, 
during a series of tests with one concentration of a salt, the latent period for a number 
of tests would be consistently about one second. Then, for no obvious reason, the 
reaction would follow a latent period of perhaps 1.8 seconds. At other times it might 
shift from long to short; or two separate and distinct reactions at the two levels might 
be observed. When the tests were first made with MgCl 2 this was found to occur 
Figure 2. — Average latent period values (open circles) for solutions of 
potassium chloride of different concentrations; and the same data 
expressed logarithmically 
