254 
BULLETIN OF THE BUREAU OF FISHERIES 
QUININE SULPHATE 
The reactions of the tentacles to quinine are in every way comparable to those 
to the salts just described. The curve (fig. 7) is a typical hyperbola and the points, 
logarithmically expressed, fall around a straight line which has an angle, however, of 
less than 45°. A distinct and meas- 
urable tentacular reaction was ob- 
served as a response to concentra- 
tions as low as 0.0004 per cent. 
According to Hecht (1918) the taste 
threshold in man for quinine sul- 
phate is 0.00004 M. Since the 
oyster is sensitive to 0.0004 per cent, 
or about 0.0000046 M., the latter is 
about eight times as sensitive to this 
substance as man. 
ALKALIES 
The difficulty of working with 
alkalies in sea water is great unless 
artificial, carbonate-free sea water 
is employed. In experiments of the 
present kind it is necessary for the 
specimens to be immersed in a con- 
siderable quantity of running water 
in order to insure against building 
up of a significant concentration of the test chemical in the medium. For this 
reason it is impractical to use artificial sea water entirely. Experiments might 
be made in which the specimens are immersed in natural sea water and only 
the solution of alkali in carbonate-free water. This procedure, however, would 
probably not be satisfactory, for in order to bring about stimulation it is neces- 
sary for the test solution to come into contact with the tentacles which are already 
immersed in sea water, and reaction between the molecules of alkali and carbonate 
would take place close to the sensory surfaces. In such a case precipitation com- 
pounds would be formed. 
In these experiments such possible sources of error were recognized, but a few 
series of tests were made without attempting to eliminate the difficulties. Never- 
theless, the results appear to be of considerable significance. Stock molar solutions 
of KOH and NaOH were made in sea water. The precipitate of magnesium and 
calcium carbonate was allowed to settle and the solution decanted and filtered. 
Immediately preceding a series of tests the desired concentration was made from the 
stock solution and sea water. Again a precipitate was formed and removed by 
decanting and filtration. When the test solutions came into contact with the 
tentacles there was probably further precipitation. However, in all except possibly 
the most dilute solutions the hydroxvl-ion concentration was sufficient to remove all 
of the carbonates from the test solutions. The concentrations of alkali as stated in 
terms of mols of alkali originally dissolved, while not strictly correct, are relatively 
correct with relation to one another. 
This will appear more clearly when Figures 8 and 9 are examined. One series 
of tests each for NaOH and KOH are given in the graphs. Three such series were 
Figure 7. — Average latent period values of the response of the oyster 
to quinine. On the same graph (solid points) the data are expressed 
logarithmically 
