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, 1 are placed in n/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. 



From M/100 cone. 



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. 2 



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 



'Harvey, 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. 



