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BULLETIN OF THE BUREAU OF FISHERIES 
Crozier (1915) studied by means of reaction times and threshold concentrations 
the responses of Holothuria surinamensis to salts, acids, carbohydrates, and alka- 
loids. Similar observations have been made by Olmstead (1917) on Synaptula; 
Hecht (1918) on Ascidia; Crozier and Arey (1919) on Chromodoris ; Arey and Crozier 
(1919) on Chiton; Agersborg (1922) on Nudibranchs; Copeland (1923) on Palaemo- 
netes; Copeland and Wieman (1924) on Nereis; and various others. A recent review 
of the significant findings of these workers is that of Parker and Crozier (1929). 
MATERIAL AND METHODS 
The experiments described in the following pages were made at the biological 
laboratory of the United States Bureau of Fisheries at Beaufort, N. C. Large local 
oysters ( Ostrea virginica ) were employed. 
By sawing through the posterior portion of the right valve of a specimen, it was 
possible to remove the severed piece of shell without injury to the underlying tissues. 
The mantle, with its border of 2 rows of tentacles, 2 to 5 millimeters long, was in 
this manner exposed. The method by which a chemical solution was brought into 
sudden contact with the tentacles has already been described (Hopkins, 1932). By 
means of an arrangement of constant levels a stream of water flowed through a 
small tube across a few tentacles. By making a quick turn of a 3-way stopcock 
the stream of water was suddenly replaced by the chemical solution to be tested. 
The total time from turning of the stopcock until the retraction of the tentacles 
was measured with a stopwatch. The time required for the solution to go from the 
stopcock to the tentacles was measured by use of a colored solution. This value 
was then subtracted from the total time measured, giving the actual latent period, 
or the time required for the reaction to take place after the solution reaches the 
tentacles. 
The test solutions were made up in sea water so as to eliminate any possible 
effect of distilled water. When stimulated by a chemical solution the tentacles of 
the oyster retract sharply, so that the latent period may readily be measured. The 
reaction to distilled water, or to sea water diluted with equal parts of distilled water, 
or to sea water concentrated to half its original volume, is quite different. In these 
cases the tentacles retract very slowly, and it is almost impossible to determine the 
time of beginning of the movement. This is in marked contrast to the quick jerk 
of the tentacles when stimulated by an irritating solution and is clear evidence that 
the latent periods determined in the experiments were not due to differences in 
osmotic pressure. 
EXPERIMENTAL OBSERVATIONS 
No attempt has been made to list all substances which may stimulate the oyster. 
The purpose of the experiments was to find out how the reaction time varies with 
concentration in enough types of compounds to indicate whether the same principles 
obtain in all cases. One substance was tested which in man is an adequate stimulus 
for the sense of smell, namely, cumarin. This has an odor similar to that of vanilla 
and at fairly high dilutions, at least, seems to have no taste as distinct from odor. 
As representatives of substances commonly identified with the sense of taste 
the following compounds were employed: Several inorganic salts; quinine sulphate; 
cane sugar; hydrochloric acid (though these results were not totally satisfactory 
because of the difficulties concerned with acid in sea water); and alkalies, namely, 
