242 CAROTINOIDS AND RELATED PIGMENTS 



The formation of crystals in plant tissues by the methods described 

 is alone sufficient for a gross identification of carotinoids. For veri- 

 fication, however, the crystals may be treated either with strong 

 H,S0 4 or bromine water or with a solution of SbCl y in 25 per cent 

 HC1. In each case the reagent will impart a blue color to caroti- 

 noid crystals of all types. When using the antimony reagent the prep- 

 aration must first be placed in dilute HC1. In the other cases the prep- 

 aration may be placed in a minimum amount of water. 



The differentiation of the types of crystals as xanthophyll, carotin 

 or lycopin, rests upon two general tests which are reasonably accu- 

 rate. (1) Xanthophyll crystals dissolve very quickly in a phenol- 

 glycerol mixture made up of 3 parts by weight of phenol and 1 part 

 by weight of glycerol, while carotin and lycopin dissolve very slowly 

 if at all. Van Wisselingh found that carotin crystals from carrots 

 and lycopin crystals from tomatoes remained untouched by this re- 

 agent even after several days. (2) Xanthophyll crystals give a quick 

 blue color when treated with 75 per cent H 2 S0 4 while carotin and 

 lycopin crystals require a stronger H 2 S0 4 to color their crystals blue, 

 or at least to do so quickly. 



Animal tissues. The possibility of a microchemical demonstration 

 of carotinoids in animal tissues rests at the present time on the as- 

 sumption that the methods which have been used for identifying lipo- 

 chromes in such tissues are in reality methods for detecting caroti- 

 noids, and are, moreover, specific for these pigments. Let us see 

 whether these assumptions are justified. 



Two methods have been used rather generally for detecting lipo- 

 chromes in sections of animal tissues. One has been the application 

 of the so-called specific color reactions with concentrated H 2 S0 4 and 

 HN0 3 and with iodine-potassium-iodide solution; the other has been 

 the reaction of the pigments towards certain fat stains, particularly 

 Scarlet Red, Sudan III and osmic acid. 



Carotinoid pigments are encountered in animal tissues both as intra- 

 ccllular and intercellular substance, generally in more or less gran- 

 ular or amorphous condition but also coloring what appears to be true 

 fat globules. The possibility is also not excluded that they may oc- 

 cur in the tissues bound to protein as they at times occur in the blood. 

 Since carotinoids dissolve readily in liquid fats, one may also expect 

 to find fats at times dissolved in carotinoids. It is therefore an open 

 question whether true lipochromes (carotinoids) ever occur in ani- 

 mal tissues in a pure condition. Since lipochrome is never encoun- 



