126 CAROTINOIDS AND RELATED PIGMENTS 



luteohamatoidin or hacmolutein, while Holm called it hamatoidin. Of 

 the two papers mentioned that of Holm, only, has been accessible to 

 the writer. It is gratifying to note how accurately Holm described 

 the crystalline form, the color of the crystals, both alone and when 

 dissolved in various solvents, and the characteristic blue color reac- 

 tion with nitric acid, all of which later helped to identify the pig- 

 ment as carotin. The close relationship of the corpus luteum pig- 

 ment to other yellow pigments in plants and animals was first recog- 

 nized by Thudichum (1869), but his supposition that most of these 

 pigments were identical has since proved to be without foundation, 

 although his ideas in this respect were in part correct. 



Capranica (1877) likewise isolated the corpus luteum pigment from 

 cow's ovaries and obtained it in crystalline form. The general prop- 

 erties (color reactions, spectroscopic absorption bands and solubility) 

 corresponded so closely with those of the pigment of the yolk of eggs 

 (hen) and the pigment in the retina of the eyes, as examined by this 

 investigator, that he regarded the three pigments as identical. This 

 conclusion led him to regard this pigment as one of the most impor- 

 tant substances in living matter. The following quotation from 

 Capranica's paper is, to say the least, the most enthusiastic concep- 

 tion of the part which carotinoids play in animal life, which the writer 

 has encountered. "Diese Substanz muss demgemiiss als eine der 

 phylogenetisch altesten chemischen Verbindungen des thierischen 

 Korpers angesehen wcrden. Wir diirfen annehmen, dass schon in den 

 ersten Regungen der organischen Materie das lichtempfindliche Mole- 

 cul des Lutein vorhanden sein. Die erste Entstehung dieses Moleciils, 

 kann man sich denken, war das 'Fiat Lux.' Mit ihr begann zwischen 

 Sonne und organischer Materie jene empfindende Verbindung, als 

 deren letzte und hb'chste Frucht wir des Menschen sonnenhaftes Auge 

 anstaunen." 



The full significance of Capranica's contributions, however, was not 

 appreciated by him or by subsequent investigators of animal chromo- 

 lipoids. He observed, among other things, that petroleum ether and 

 carbon disulfide, respectively, would quantitatively remove the cor- 

 pus luteum pigment from its alcoholic solution. The development of 

 the technic for separating carotin from other pigments by this method 

 is a comparatively recent achievement, as shown in the preceding 

 chapters. If Capranica had thought to apply this test to the egg 

 yolk pigment which he had under investigation he would have dis- 

 covered a difference which may have led to a much earlier discovery 



