284 SELIG HECHT 
cotton was saturated with a concentrated solution, which was then 
applied in the same way as the crystal, and with the same result. 
By trying many substances in this way, it soon became clear that 
Nagel was very far from the truth when he denied a chemical 
sense to ascidians. Ascidia responded to all the acids, bases, salts, 
alkalcids and anesthetics with which I made preliminary tests. 
It was, however, not my aim to make an exhaustive qualitative 
survey of this type of irritability. The effects of various sub- 
stances on protoplasm have already received sufficient attention 
to enable one to classify them broadly into certain groups. There- 
fore, a representative number of substances from each of these 
groups were chosen for study, not so much with a view to deter- 
mine their individual properties, but rather with a desire to com- 
pare quantitatively their effectiveness in producing the same 
response. In this way it was hoped to interpret the physiologic 
nature of the chemical receptors in terms of the modern concepts 
of the physical chemistry of cells and tissues, much as Cushney 
(16) has suggested the consideration of the finer chemistry of 
protoplasm in terms of the recent work in pharmacology. 
2. Method 
Ascidia is sensitive to fresh water; therefore the materials to 
be tested were dissolved in seawater. Because of the low con- 
centrations which were necessary, the osmotic pressure of the 
seawater was increased but slightly... Moreover, the animals 
are sensitive only to large changes in the osmotic pressure. 
Seawater is a balanced solution. The addition of an electro- 
lyte already present in it, tends to disrupt the balance, making 
the augmented substance the dominant factor in stimulation. 
Undoubtedly the effect of the same concentration of a substance 
in distilled water is greater than in such a partially balanced me- 
dium. However, the results which I obtained are so similar to 
those ordinarily secured in physiologic experiments by the 
use of single electrolytes, that I am inclined to assign little value 
to this source of error. 
