January 27, 1922] 



SCIENCE 



101 



To quote briefly without essential change 

 from my previous paper : 



In a gelatine solution containing bichromate, 

 when silver nitrate is added, concentric rings 

 are formed because the ion in the gelatine is 

 relatively fixed. The silver ion wanders out 

 and forms a ring by precipitation. A region 

 on the chromate side of the ring is freed from 

 the chromate ion, and a corresponding region 

 on the silver side is freed from the silver ion. 

 Growth stops until the silver again wanders 

 out through the precipitate, and comes within 

 range of the chromate ion when the process is 

 repeated. The essentials of this interrupted 

 growth theorj' are given in the previous ar- 

 ticle. Holmes' ^ theory closely resembles mine. 

 Bradford's assumes unnecessary facts to ex- 

 plain the phenomenon. Later, I expect to give 

 a more detailed account of this common phe- 

 nomenon. 



Hugh A. McGuigan 

 University or Illinois, 

 College op Medicine, 

 Chicago 



SPECIAL ARTICLES 

 THE IDENTITY OF CERTAIN YELLOW PIG- 

 MENTS IN PLANTS AND ANIMALS 



Little attention seems to be paid, from the 

 physiological standpoint, to the fact that the 

 yellow pigments in certain animal organs have 

 been shown to be chemically identical with the 

 yellow pigments common in plants. 



Some cases of the identity of lipochromes 

 (yellow pigments of animals) with carotinoids 

 (carotin, xanthophyll, lycopersicin, and fucox- 

 anthin of plants) have been known for several 

 years,! and the list has recently been greatly 

 extended. The lipochromes of the following 

 animal tissues are now known to be either 

 chemically identical or isomeric with caro- 

 tinoids — the ear lobes, beaks, shanks, body fat 

 and blood serum of fowls, and the yolks of 

 their eggs;^ and the fat of the body, blood 



iProc. Roy. Soe. London, 72: 165. 1903. 

 Z. Physiol. Chem., 74: 214. 1911-12. 

 2 Jour. Biol. Chem., 23: 261-279. 1915. 



6 Holmes. Journal American Chemical Society, 

 1918, XL, p. 1187. 



serum, corpus luteum and milk of the cow.^ 

 It seems probable that the same is true of the 

 nerve cells of some animals and of the blood 

 plasma and body fat of the human body.* 

 These pigments are not synthesized by the ani- 

 mals, but are merely taken up from their food. 



It is well known that carotin (C^oH^g) is a 

 highly unsaturated hydrocarbon. It has been 

 shownS that part of the unsaturated linkage 

 of its molecule is of a type that can be easily 

 satisfied by direct addition of oxygen. Xantho- 

 phyll is carotin dioxide (C^^H^gO,). Lycoper- 

 sicin has the same empirical formula as caro- 

 tin. Fucoxanthin (C^^H^jO^) contains more 

 oxygen than the others. The first two of these 

 pigments are widely distributed in jDlants. Not 

 only do they always accompany chlorophyll, 

 but they are also found in flowers, fruits, seeds, 

 and subterranean organs, and also in fungi.^ 



The physiological significance of the caro- 

 tinoids has, of course, not been wholly neglected. 

 It is commonly pointed out^ that the tendency 

 of carotin to unite with oxygen may be sig- 

 nificant in connection with photosynthesis, 

 which is a reduction process. Steeiiboctf has 

 suggested that the fat-soluble vitamine is iden- 

 tical with some of the carotinoids, while Pal- 

 mer' has cited eases that seem to cast doubt 

 on this view. Tears ago Schuneki" suggested 

 the question as to whether xanthophyll, being 

 present in connection with both chlorophyll and 

 haemoglobin, may not be of physiological im- 

 portance in both cases. 



Emphasis is commonly laid on the chemical 

 similarity between the chlorophyll molecule and 

 the haemoglobin molecule, though similarity of 

 function between the chlorophyll of plants and 

 the haemoglobin of animals does not seem to 

 have been definitely shown. An examination 

 of half a dozen recent and standard works deal- 



3 Ibid., 17: 191-263. 1914. 



4 Jour. Amer. Med. Assn., 74: 32-33. 1920. 



5 Thatcher. The Chemistry of Plant Life. 1921. 



6 7PaIladin's Plant Physiol. Livingston, p. 19. 

 8Sci. N. S., 50: 352-353. 1919. 



' 9Soi. N. S., 50: 501-502, 1919, :ind Jour. Biol. 

 Chem., 46: 559-577, 192L 



loProc. Boy. Soc, London, 72: 176. 1903. 



