CAROTINOIDS IN THE VERTEBRATES 141 



of the pigments is concerned. Unfortunately no modern investigation 

 of these pigments has been made, so that it is necessary to rely on 

 the observations of those who were unfamiliar with the possibility of 

 their being related to plant carotinoids. The blue color reaction of 

 the lipochromes with iodine was introduced by Schwalbe (1874) in 

 connection with these retinal pigments. The splendid early work of 

 Capraniea 1 1877) on the chromolipoids of the corpus luteum and egg 

 yolk was undertaken primarily to study the yellow to red retinal pig- 

 incut < of amphibians and birds. He found a complete correspondence 

 between the retinal pigments of birds and those of the egg yolk. 



Kiihne contributed several papers on the retinal pigments, which 

 appeared in the memoirs of the Physiological Institute of the Uni- 

 versity of Heidelberg. Reference has already been made to the only 

 one of these papers which has been accessible to the writer (Kiihne, 

 1878), which is presumably the only paper reporting Kiihne's study 

 of the chemical and physical properties of the pigments. According 

 to this investigator the microscope reveals oil globules of three colors 

 in the retinal epithelium of fowls, namely red, yellow and greenish- 

 yellow. Kiihne's study of these globules led him to conclude that 

 three distinct pigments were involved, which he called rhodophane, 

 xanthophane and chlorophane, respectively. The evidence for the 

 existence of three pigments was based on the observations: (1) that 

 when a dry sodium soap was prepared of the orange-red ether extract 

 of the retinas and submitted to successive extractions with petroleum 

 ether, ether and benzene until each solvent extracted no more pigment, 

 the extracts were, in succession, yellowish-green, orange and rose-red 

 in color; (2) the chlorophane in the yellowish-green petroleum ether 

 could be purified from admixed xanthophane by repeated evaporations 

 and extractions with petroleum ether, giving solutions more and more 

 green in color; (3) the xanthophane in the orange ether extract could 

 be purified from admixed chlorophane by treating the ether residue 

 with petroleum ether (not, however, without some loss of xantho- 

 phane), and from admixed rhodophane by treating the chlorophane- 

 free xanthophane with CS,, in which the rhodophane was not soluble; 

 (4) spectroscopic examination of the purified pigments showed marked 

 differences, the chlorophane showing two bands, the other two pig- 

 ments only one. It is difficult to decide from these and other less 

 important points mentioned, what kinds of carotinoids are involved. 

 Save for the green color emphasized by Kiihne, one might be led to 

 believe in the light of our present knowledge that his chlorophane is 



