REGULATORY SUBSTANCES 517 



referred to and as often questioned. Their chemical relationship 

 is established by the structural similarity between chlorophyll a 

 and the blood pigment hemin. 



Yet another group of pigments, long known in plants but only 

 of late attaining prominence in animals, are the flavones. Im- 

 portant also are the flavins. The former are yellow pigments 

 familiar as dyestuffs; they occur as glucosides in combination 

 with glucose. Flavone appears to be the mother substance from 

 which come many plant pigments (such as quercetin from Quer- 

 cus tinctorius). The flavins are yellow animal pigments of no 

 chemical relationship to the flavones. Ellinger describes ovo- 

 flavin and lactoflavin, the latter forming orange-red crystals. 



Willstatter has shown a close relationship to exist between the 

 flavonal pigments and the anthocyanins. The flavones are 

 structurally related to the anthocyanins. The following for- 

 mula is given for the chloride of cyanin : 



CaTHgiOieCKCisHnOeCl + 2C6H,206 - 2H2O) 



The term anthocyanin was first introduced by Marquart, in 

 1835, to designate the blue pigment of flowers. Later, the red 

 and purple (magenta) pigments were found to be of the same 

 chemical constitution but existing in another form. The 

 terminology now generally accepted is "anthocyanin" for the 

 red, magenta, and blue glucoside pigments and " anthocyanidin " 

 for the nonglucoside form. The glucoside in the cornflower is 

 cyanin; and its sugar-free form, cyanidin. Agreement in termi- 

 nology for the yellow animal pigments has been attained by 

 calling the whole group "lyochromes"; and their individual speci- 

 mens, "flavins." 



Animal pigments play a prominent role as part of the blood. 

 Hemoglobin is the pigment responsible for the transportation of 

 oxygen. In the oxidized form, as oxyhemoglobin, it is reduced 

 through the liberation of oxygen; as a base, it neutralizes the 

 carbon dioxide which the tissues give off. (There is some ques- 

 tion as to this so-called oxidation. It appears that no true 

 oxidation takes place but that the oxygen is, instead, simply 

 adsorbed by the blood, i.e., by the hemoglobin or the iron in it, 

 and carried from the lungs to the tissues where it is given up, no 

 change taking place in valence of the iron.) The two chief con- 

 stituents of the blood pigment hemoglobin are hemin and globin. 



