20 



PHYSIOLOGY OF NUTRITION 



Willstatter and Mieg. 1 This pigment forms fiat, rhombic crystals, which, with 

 one-sided illumination, appear blue-green on the illuminated side and orange- 

 red on the other. It is readily soluble in ether, chloroform and carbon bisul- 

 phide, less so in benzine, slightly soluble in hot alcohol, almost insoluble in cold 

 alcohol and insoluble in water. A carbon bisulphide solution of carotin is 

 blood-red; dissolved in concentrated sulphuric acid, carotin is bluish- violet. It 

 is a hydrocarbon, with the formula C 4 oH 5 6, which is easily oxidized. It may be 

 transformed into cholesterin. The carotin content of leaves varies with the 

 season of the year. A series of experiments continued throughout the summer 

 upon the leaves of stinging nettle and horse-chestnut showed that the carotin 

 content is greatest during the flowering season, for both plants. The formation 

 of carotin is also dependent upon light; green leaves of vetch contained 178.8 

 mg. of carotin, as compared to 34.0 mg. in the same quantity of etiolated leaves. 



3C J) Eb F G 



: 1 



Lycopin 



Karotin 



III Mil 

 70 65 60 



p IG I0 — Absorption spectra of carotin and lycopin. {After Escher.) The Fraunhofer 

 lines are indicated by the letters above and the wave-lengths (in 10 w) are shown below; the 

 thickness of layer employed is given (in mm.) at the left. 



It was shown by the work of Kohl 2 that carotin is widely distributed. It 

 is not limited to the green parts of plants but occurs also in flowers, fruits, seeds 

 and subterranean organs, and also in fungi. It may be extracted in large quan- 

 tities from carrots. 



The function of carotin is not yet clear, but its tendency to unite with oxygen 

 appears, at any rate, to be significant in connection with the photosynthetic 

 process, where reduction of compounds containing oxygen is known to occur. 

 The absorption spectrum of carotin has two dark bands in the green-blue half of 

 the spectrum (Fig. 10). 



A second yellow pigment accompanying chlorophyll is xanthophyll, an oxida- 

 tion product of carotin, with the formula C4oH 56 2 . 1 



1 Willstatter, Richard, and Mieg, Walter, Ueber die gelben Begleiter des Cholorophylls. Liebig's Ann. 

 Chem. u. Pharm. 355= 1-28. 1907- 



2 Kohl, Friedrich Georg, Untersuchungen uber das Karotin und seine physiologische Bedeutung in der 

 Pflanze. Leipzig. 1902. 



l "The absorption spectra of carotin and xanthophyll, as given by Willstatter and Stoll 

 (1913) [see note b, p. 7] are here reproduced as Fig. 11. It is questionable whether xanthophyll 

 is actually formed by the oxidation of carotin. — Ed. 



