of the Salmon in Fresh Water. 161 



The yellow pigment remains in the caustic solution, from which it 

 cannot be extracted by ether or petroleum ether. It is not precipitated 

 by the addition of acid, but the solution is then decolorized. 



CHABACTERS OF PIGMENTS. 



The above observations show that the red flesh of the salmon contains 

 two pigments, of which one is pink, and gives the blue lipochrome 

 reaction, while the other is yellow, and does not give this reaction. 



An investigation of the mature ovaries conducted in precisely similar 



fashion showed that in them also two pigments a red and a yellow 



combine to produce the normal coloration of the organs. 



The Red Pigment. The characters of this red pigment are as follows: 

 It is a lipochrome pigment, giving a blue colour in the dry state with 

 nitric or sulphuric acid, and is soluble in alcohol, ether, benzol, petroleum 

 ether, and acetic acid. Except in ether and petroleum ether, the solu- 

 tions are of a pink or reddish colour, while these two solvents form pure 

 yellow solutions. If the solutions are evaporated, the pigment recovers 

 its red colour as the last drop of the solvent disappears. 



The pigment forms compounds with caustic soda and potash, which 

 are soluble in dilute alkaline solutions, at least in the presence of soaps. 

 From these solutions the pigment may be precipitated by the addition 

 of dilute acetic acid, or may be directly extracted by means of ether. 

 Similar compounds are formed with lime and baryta. 



The pure dry pigment fades very rapidly either in light or in dark- 

 ness. Solutions also fade, but much more slowly. The loss of the power 

 of giving a blue colour with concentrated acid is one of the first signs 

 of change, and it may occur before the loss of colour in the solution is 

 obvious. Pigment dissolved in benzol seems especially liable to undergo 

 this change. 



As to its other characters, solutions of the pigment when examined 

 with a microspectroscope exhibit an indefinite shading in the neighbour - 

 hoodof the F line, but this is hardly visible when the solutions are 

 examined with a spectroscope of larger dispersion. In this case there is 

 merely continuous absorption of the violet end. 



As a whole, the pigment corresponds closely to the lipochrome pig- 

 ment described in various animals, and notably in Crustacea, as tetro- 

 nerythrin or zoonerythrin (by Moseley as crustaceorubrin). From the red 

 pigment of the lobster the pigment differs slightly in tint and in the 

 solubility of the sodium compound, but it is uncertain how much stress 

 should be laid upon these differences. 



The Yellow Pigment. The yellow pigment does not give the lipochrome 

 reaction. It belongs to a group of pigments which are apparently exceed- 

 ingly widely distributed in the animal kingdom, but which have been little 

 investigated. They have been commonly confounded with the lipo- 

 chrome pigments. In the salmon the pigment occurs in the muscle, the 

 ovary, and in large amount in the liver. It is always in close associa- 

 tion with fat, and its solubility seems to depend upon that of the 

 associated fat. In the salmon the pigment is associated with the fat 

 olein, which is soluble in methylated spirit, and the pigment is also 

 soluble in this solvent. In the case of bright yellow fat obtained from 

 a cow, a pigment of otherwise identical characters was very little 

 soluble in cold methylated spirit, but dissolved readily in ether. 

 The fat with which the pigment was associated was here stearin and 

 not olein. 



The yellow pigment does not apparently form compounds with the 

 alkalies or alkaline earths. It remains in the ether when an ethereal 



