154 Papers from the Department of Marine Biology. 
xylol, within the cells of the “prickly fish.” In that case a weakly 
dissociated acid if quite lipoid-soluble would change the color of an 
indicator in the lipoid, while a weak, less lipoid-soluble acid would not. 
This fact can be demonstrated very nicely by the use of droplets of 
benzol or chloroform containing Nile blue in solution. Both these fat 
solvents take up the dye in the red condition, while the color of the dye 
in acid solution is blue. If red benzol droplets of Nile blue, made by 
shaking the benzol solution with egg albumen,’ are placed in 7/10 
solutions of acetic, propionic, butyric, and valeric acids, it is only in 
n/10 valeric acid that the droplets become blue. Despite the fact that 
valeric acid is a very weak acid, enough will enter the benzol to unite 
with the free red Nile blue base and form a salt blue in color. The same 
is true of the still weaker acid, ortho-amino-benzoic. Not enough 
acetic, propionic, or butyric acid can enter to do this. On the other 
hand a strong acid, such as trichloracetic or dichloracetic, even though 
very slightly lipoid-soluble, is able to cause the color change in n/10 
concentration. Monochloracetic is not quite strong enough to do this. 
TABLE 5. 
Pro- Mono- | pichlo- | Trichlo- 
4 . = if - . 1 c = ° 
Acid. Acetic. pionie. Butyric.| Valeric. | Caproic.) Formic.| chlo Sp ee STAG, 
racetic. 
Cone. forcolorchange.| /20 n/40 n/80 n/160 | n/320 | n/320 | n/2560 | n/5120 |n/10240 
Dissociation constant, 
K 0.155 | 5.14 121.0 
Partition coefficient 
XvlolXwater from 
M/10 cone il. : : 3.07 il. .O1 
*From M/100 conc. 
That both lipoid solubility and degree of dissociation are also factors 
in determining the color change of chloroform drops containing Nile 
blue is shown (table 5) when we compare the concentration of acids 
required to turn the drops red blue in color.’ 
The result is similar to that with benzol, except that less acid is 
required to change the color, due possibly to the fact that chloroform 
will dissolve some water in which the acids may dissociate. A strong 
acid (chloracetic acid and formic acid) will affect the indicator in chlo- 
roform even if very slightly lipoid-soluble, or a lipoid-soluble acid 
(caproic) will affect the indicator even though very weak. Carbon 
disulphide and carbon tetrachloride globules act similarly to chloro- 
form globules. 
However, the purple pigment of Stichopus ananas is certainly not 
in fat or oil bodies of any kind or in fat solvents. The indicator is 
water-soluble and no trace of the bodies holding it remains after the 
\1Harvey, Amer. Journ. Physiol., 6, p. 340, 1913. 
°The series of acids for penetration into chloroform agrees to a certain extent with the penetra- 
tion series for cells. The parallelism is not exact. 
