294 SELIG HECHT 
The physiological inertness of the sugars is known only too 
well to require more than mention. Their ineffectiveness has 
made their use possible in experiments where the effect of osmotic 
pressure only is desired (Hoéber, 714, p. 496). It is therefore 
altogether in keeping with the parallelism between genera! phys- 
iological activity and sensory stimulation that Ascidia fails to 
be stimulated by even high concentrations of glycerin and sucrose. 
It has been suggested that the sensory inactivity of the sugars 
may be due to the lack of these substances in an aquatic environ- 
ment (Parker, °12). The improbability of the occurrence of 
saccharin in the seawater, however, does not prevent its chemical 
stimulation of Ascidia. The liminal concentration of a commer- 
cial preparation was 0.025 M, to which the usual negative re- 
sponse was given. 
It is necessary, similarly, to look in a different direction for the 
explanation of the sensitivity of Ascidia to alkaloids and anes- 
_thetics. The minute quantities of alkaloids which are effective 
in stimulation find their counterpart in the extremely low con- 
centrations in which they penetrate cells (Overton, ’97). 
As a consequence of these results there can be no doubt of the 
essential similarity between the general physioiogical reactions 
of chemical substances and their effects on the sensory processes 
in Ascidia. This indicates that the action of the stimulating agent 
on the sense organ involves an effect of the same nature as the 
action of these substances on other cells and tissues. Moreover, 
it shows that the effect of a chemical on the receptor concerns 
that structure primarily as a cell, and only secondarily as an 
organ for receiving stimuli. 
It must be emphasized that these generalizations are not 
intended for the sense of taste in vertebrates, but solely for the 
sensitivity of animals, like Ascidia and Holothuria, which possess 
a general chemical sense. This type of irritability corresponds 
in many ways to the common chemical sense of vertebrates 
(Parker, ’12), although the two need not necessarily be homolo- 
gous. ‘The problems involved in the higher organs of taste, par- 
ticularly the sweet taste, do not concern us here. They represent 
specialization for certain needs; and in the present condition | 
