THE PERMEABILITY OF CELLS FOR ACIDS." 
By E. Newton Harvey. 
The results of researches on the permeability of cells for alkalies, 
using the color change of an indicator, neutral red, within the cell as 
a convenient method of detecting penetration of the alkali, were pub- 
lished’ by the present author in 1911. Bethe’ and also Warburg! had 
used the same method for certain of the alkalies, although I was un- 
aware of their experiments at the time. Bethe likewise found that if 
meduse (Rhyzostoma) are stained in neutral red, they become orange 
red in color and if HCl is then added to the sea-water the orange red 
does not change to bright red until the tissues are killed. In the 
meantime, loss of irritability on the part of the muscles has occurred 
while the neutral red dye is still orange red in color. In my experience 
neutral red has always been taken up by cells in a bright-red condition, 
so that acid, if it entered the cell, would produce no further marked 
color change. I have found it likewise impossible to stain living cells 
with any other dye which will act as an indicator for acid. 
Plant cells containing blue or purple anthocyan pigments will turn 
red in acids, and Pfeffer’? found that purple Tradescantia or Pulmonaria 
cells become red in an “‘dusserst verdiinnte”’ solution of HCl, H,SOx, 
and acetic acid, and the purple color returns when the acid is washed 
out; nor is the cell killed, as protoplasmic rotation also returns. The 
same result has been obtained by Ruhland.® It is difficult to judge 
of these results because exact molecular concentrations are not given, 
but they seem opposed to Bethe’s experiment on meduse. Plant 
pigments are difficult to work with for two reasons: (1) The plant cell 
is usually cuticularized and is not readily wet by the acid solution; 
(2) anthocyan pigments are not equally sensitive to both weak and 
strong acids. 
The experiments recorded in this paper were all made with the tissues 
of a holothurian, Stichopus ananas, the “prickly fish’ of the Beche 
de Mer or Trepang industry. A concentrated solution of dark-red 
pigment is found in irregular sacs or bodies of unknown nature just 
under the epithelium of practically all the internal organs. It is 
especially abundant on the gonads, although the eggs and sperm cells 
are colorless. Living portions of the testis stained in Schneider’s 
1Contributions from the Torres Straits Expedition of the Carnegie Institution of Washington 
and the Physiological Laboratory of Princeton University. 
2Journ. Exp. Zool. 10, p. 507, 1911. See also Carnegie Inst. Wash. Pub. No. 183. 
3Pfluger’s Archiv, 127, p. 261, 1909. 
4Zeit. f. Physiol. Chem., 66, p. 305, 1910. 
5Osmotische Untersuchungen, p. 140, 1877. 
6Jahrb. f. Wiss. Bot., 46, p. 1, 1908. 
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