GENERAL DISTRIBUTION OF CAROTINOIDS 17 



merated. KrukenlxTg believed that all lipochromes should be regarded 

 as composed of carbon, hydrogen and oxygen, and free from nitrogen. 

 At the present time hydrocarbons, such as carotin and its isomers, 

 as well as the oxyhydrocarbons, fulfill all the characteristics of lipo- 

 chromes. Probably wider use has been made of the color reactions 

 with concentrated sulphuric and nitric acids and with iodine in potas- 

 sium iodide than any of the other class characteristics for identifying 

 pigments as lipochromes although many studies have also included 

 spectroscopic observations. Unfortunately the color reactions and 

 spectroscopic properties are subject to greater variation than any of 

 the others upon which the classification is based. The result of the 

 color tests as well as the quality of the color is often influenced 

 strongly by admixture with foreign substances, and this is apparently 

 especially true for the reaction with iodine in potassium iodide. Simi- 

 larly the spectroscopic absorption properties are subject to wide varia- 

 tion as to the position of the bands as well as their definiteness by 

 reason of admixture with impurities, concentration of pigment, and the 

 solvent employed. 



Lipoxanthins 



A more recent attempt than Krukenberg's to bring all the known 

 plant and animal pigments with like properties under one name is 

 that of Schrotter-Kristelli (1895a), who proposed to group together 

 all the various plant and animal coloring matters which had previously 

 been known as etiolin, chlorophyll yellow, xanthin, anthoxanthin, 

 lutein, xanthophyll, chrysophyll, carotin, phylloxanthin, phycoxanthin, 

 erythrophyll, solanorubin, lipoxanthin, haematochrom, ehlororufin, 

 bacteriopurpurin, haemolutein, vitellorubin and tetronerythrin. He 

 regarded these pigments as at least an homologous group, if not com- 

 pletely identical, and chose the name lipoxanthin as the most suitable 

 for a general designation. The chief characteristics of the lipoxan- 

 thins, according to Schrotter-Kristelli, arc their affinity for fats, their 

 insolubility in water, their blue color reaction with concentrated sul- 

 phuric acid, their absorption of the violet end of the spectrum, their 

 lack of fluorescence when in solution, and their ease of destruction by 

 light and oxygen. Schrotter-Kristelli believed that the slight dif- 

 ferences in the spectroscopic properties of the various pigments were 

 due to their ease of destruction. 



According to this author lipoxanthins have been demonstrated to 

 occur in all green leaves, in autumn leaves, in many flowers and fruits, 



