PROPERTIES AND METHODS OF IDENTIFICATION 247 



chloride in 50 per cent alcohol was especially suitable for this pur- 

 pose. Treatment o!' sections showing carotinoid grannies with hydro- 

 gen peroxide tor 24 to 48 hours apparently effected the same result, 

 but Dr. Pulley's recent communication indicates that the oxidation 

 is not so thorough as with the ferric chloride unless the peroxide is 

 supplemented with strong sunlight. There is also the tacit assumption 

 among pathologists that sections which give up their pigment to fat 

 M>1 vents contain lipochromes. This, of course, can only be considered 

 contributory evidence. 



Summary 



It is impossible to summarize adequately in a few words the facts 

 presented in this chapter describing in detail the chemical and physi- 

 cal properties of the several carotinoids both in crystalline form and 

 also when in solution in various solvents. 



It may be pointed out, however, that the properties of impure 

 solutions of the individual carotinoids when freshly prepared are suf- 

 ficiently characteristic for their identification without resorting to the 

 tedious process of isolating the pigments in pure crystalline form. The 

 characteristic properties which may be employed for this purpose in- 

 clude color, spectroscopic absorption bands, relative solubility in al- 

 cohol and petroleum ether and adsorption affinity towards finely di- 

 vided agents like CaC0 3 . 



It is fortunately possible to identify carotinoids in general in plant 

 issues through a microchemical crystallization method. It is possi- 

 ble, also, to roughly differentiate these crystals into groups, such as 

 carotin, xanthophyll and lycopin-like pigments, by means of the ef- 

 fect of a phenol-glycerine solvent on the crystals and the rapidity 

 with which they respond to a color reaction with sulfuric acid of 

 different strengths. 



The microchemical demonstration of carotinoids in animal tissues 

 does not rest on a very adequate basis. Recent work, however, indi- 

 cates that although it is not possible to differentiate between carotinoid 

 pigment and fatty acids, these can be distinguished from neutral fat 

 and esters by means of their characteristic staining reaction with Nile 

 blue, the former staining blue and the latter some shade of pink. 



