146 Papers from the Department of Marine Biology. 
aceto-carmine show regular epithelial nuclei and just below them the 
pigment bodies which have no special nuclei connected with them. 
Whatever their nature, acid must diffuse through an epithelium of 
living cells to reach them. So long as the cells are living the pigment 
remains in them, but if killed by heat or distilled water or chloroform- 
saturated sea-water or acid or alkali, the pigment passes out, 7. e., they 
cytolyse and, asin so many other pigment-containing cells, the coloring 
matter diffuses away. 
The chemical nature of the pigment is unknown. It is water soluble 
and fairly unstable, decomposing into brownish compounds at 100° C. 
If dissolved in sea-water and HCl is slowly added, it changes in color 
from dark red to orange when the concentration of acid becomes 
n/1000 to n/500. The color change is very nearly but not quite as 
marked in a weak acid like butyric. On the addition of alkali the color 
becomes purple. Moseley’ in 1877 described a similar if not identical 
pigment from crinoids dredged in the channel between Cape York and 
Albany Island, Australia, and also from a deep-sea holothurian of 
the South Indian Ocean. He called the pigment antedonin and I 
shall adopt the same name. The echinochrome of MacMunn? and 
McClendon’ is no doubt a closely related pigment. 
TABLE 1.—Temperature about 28° C. 
Hydrochloric acid. Butyric acid. 
Concentration 
of acid. Living Dead Living Dead. 
epithelium. __ jopsthelium. epithelium. |epithelium. 
if DOr sa oe 3to 4 mins. ch aga 30 secs....... Instantly. 
MEP AD core ete 6 to 7 mins.|....do.. LOPMINA) ce 2 Do. 
WPT SOL. Rec se ae raed Re earatallifcte ce do....| 45 mins...... Do 
AB (LOO! A cee ciel) AeveOEMIA yee orcciliocoe G65.2| Po MIMS:..- 5,5. Do. 
n/IGO.. tS 20 to 25 ming:|....do.2..| 2 hours.:...: Do. 
MILB2Z0. ceecaes se 45 mins...... 30 secs 4 hours....c.<5 1 min 
In the following experiments small pieces of the branched filamentous 
testis were used. Acid was added to a neutral artificial sea-water of the 
following composition, m/2 (100 NaCl+2.2 KC]+2CaClh+10MgCl,), 
until the proper concentration of acid was obtained. Ovxalic acid pre- 
cipitates the Ca so that this acid was added to m/2 NaCl. 
A study was first made of the penetration times of a weak (butyric) 
and a strong (HCl) acid in different concentrations into living and dead 
tissue. The results are given in table 1. The tissue was killed by 
half-minute immersion in chloroform-saturated sea-water. Under 
these conditions the pigment begins to diffuse out of the cells, but 
in each case the acid penetrates before the diffusion is nearly complete. 
It will be noted that the living tissue is decidedly resistant as com- 
pared with the dead, and that the resistance varies with the acid and 
with the concentration of acid. Note that butyric acid in n/20 con- 
1Quart. Journ. Micros. Soc., 17, p. 5, 1877. 
*Quart. Journ. Micros. Soc., 25, p. 469, 1885; 30, p. 51, 1889. 
3Journ. Biol. Chem. 11, p. 436, 1912. 
