The Permeability of Cells for Acids. 147 
centration enters more rapidly than hydrochloric, but in n/40 concen- 
tration the reverse is the case. 
Why does one acid enter more readily than another? To study this 
question we must determine the penetration rates of a large series of 
acids and compare them with such physical properties as degree of dis- 
sociation, power to lower the surface tension of water, solubility in 
lipoids, adsorbability by solids, ete. A comparison of this kind follows 
in table 2. All the acids enter in less than a minute if the tissue has 
previously been killed. 
Rate of penetration into the testis of the “prickly fish” was deter- 
mined from n/100 concentration of acid. 
Percentage dissociation is calculated from Ostwald’s' conductivity 
figures, and surface-tension values are taken from Traube’s? results. 
By lipoid solubility is meant solubility in substances of fatty nature 
or fat solvents—olive oil, lecithin, benzol, etc. As a measure of lipoid 
solubility I have determined the partition coefficient of acids between 
xylol/water from 7/10 and 7/100 concentration of acid. 25 c.c. of 
approximately n/100 acid were shaken with 25 c.c. xylol. Equili- 
brium is rapidly attained. The normal concentration of the acid was 
exactly determined before shaking and after shaking by titration. 
The difference is the normal concentration of acid in the xylol. 
Cone. in xylol layer 
Cone. in water layer 
The determinations were only approximate, as no thermostat was 
used. The temperature was about 20°C. As indicated in the table, 
most of the acids will not pass to xylol from weak concentration in 
water. The values for the partition coefficients between olive oil and 
water were very kindly given me by Dr. Hardolph Wasteneys, of the 
Rockefeller Institute. The olive oil contained oleic acid equal to 
2.3 c.c. n/100 alkali per 100 c.c. and was shaken for 15 hours with the 
acid solutions. The figures for adsorbability are from Appleyard and 
Walker’s’ experiments on silk. They represent the percentage of acid 
adsorbed from 100 c.c. n/64 acid by 3 grams of silk after 42 hours at 60°. 
The limit of error is one. Freundlich‘ gives a similar series for adsorp- 
tion by animal charcoal. 
Since the testis epithelium of the “‘prickly fish” is a passive tissue, 
the toxicity of the acids could not readily be determined on it. The 
cilia of the palps of the giant clam, Tridacna gigas, very common 
along the Great Barrier Reef, were therefore used for this purpose. 
To 50 c.c. artificial sea-water was added respectively 0.1, 0.2, 0.3, 0.4, 
= partition coefficient. 
1Organic acids. Abh. d. Sachs. Ges. d. Wissensch., 15, p. 97, 1887; inorganic acids in Journ 
Prac. Chem., 32, p. 300, 1885. 
2Berichte d. d. Chem. Ges., 17, p. 2294, 1884; Verh. d. d. physikal. Ges., 10, p. 880, 1908; 
Liebig’s Annalen, 265, p. 27. 
3Journ. Chem. Soc., 69, p. 1334, 1896. 
4Zeit. Physik. Chem., 57, p. 385, 1907. 
