PHYSIOLOGY OF ASCIDIA ATRA LESUEUR 289 
Therefore, a concentration of 80 per cent seawater at the sense 
organ would probably act as a stimulus. The measured liminal 
concentration was 30 per cent seawater. On the assumption 
that this corresponds to a concentration of 80 per cent seawater 
at the receptor, the 30 per cent seawater must have been mixed 
with at least three times its volume of seawater before it reached 
the sense organs. In this way we are furnished with a rough 
value for reducing the liminal concentrations given in the fol- 
lowing experiments to a basis more nearly comparable with the 
results obtained in other physiologic processes and in the chemical 
stimulation of other animals. 
5. Results with chemicals 
Salts. The three typical salts, NaCl, KCl and NH,Cl, were 
tested in order to compare the effects of the alkali cations. In 
table 5 are given the liminal values obtained in Exp. VII.5. 
TABLE 5 
Liminal concentrations of alkali salts 
SALT CONCENTRATION 
NaCl 0.4N 
KCl 0.2N 
NH.Cl 0.3 N 
Arranged in the order of their effectiveness as stimulating agents, 
they show the familiar cation series: 
K >NH,>Na 
This parallels the stimulating strengths of these cations found by 
Cole (10, p. 607) for the common chemical sense in the frog. 
In order to determine the effects of a group of anions, the 
following salts were used: KCl, KBr, KNO;, KI, CH;COOK, 
and KSCN. The first experiments were made on small, and 
consequently very sensitive, animals. By this means large 
differences in stimulating power became evident; this is typified 
by Exp. VIII.3 of which the following table is a summary (table6). 
Later, in order to separate KCl, CH;COOK and KSCN, 
larger, and therefore less sensitive, animals were used. Exp. 
VIII.4 was of this type and gave the results shown in table 7. 
THE JOURNAL OF EXPERIMENTAL ZOOLOGY. VOL. 25. NO. 1 
