156 CAROTINOIDS AND RELATED PIGMENTS 



Our interest naturally centers around the derived "xanthophylls" 

 found in the hamolymph and other tissues, and Poulton's proof for 

 its existence. It may be stated first, however, that Poulton used the 

 word xanthopyll in a collective sense for the yellow pigments accom- 

 panying chlorophyll. The use of the word carotinoids conveys the 

 same meaning. The proof for the derived carotinoids in the larvse 

 and pupae rested largely upon a spectroscopic examination of the 

 blood extracts in comparison with the spectrum of the pigments of 

 green leaves under like conditions. Poulton's own conclusion was 

 that the points of difference between the derived "xanthophyll" spec- 

 trum of caterpillars and that of green plants made it impossible to 

 decide whether more than one derived "xanthophyll" was present. 

 Interpreted from the point of view of our present knowledge of the 

 carotinoids this means that, inasmuch as Poulton was dealing with 

 extracts for which no purifications were attempted, it is impossible to 

 decide whether carotin or xanthophyll or a mixture of carotinoids 

 causes the colors of the carotinoid type found in caterpillars. 



It is impossible to review Poulton's entire paper. There is one 

 further point, however, which may throw some light on the character 

 of the carotinoids taken up by these insects and which at least forms 

 an interesting link between carotinoids as found in mammals and the 

 same pigments in caterpillars. This point is the great stability of 

 the "xanthophyll" in the blood of these insects, which led Poulton to 

 believe that it "may be due to association with a protein of the 

 blood." Poulton found that ether, chloroform and carbon disulfide 

 would not extract the pigment from the blood, although the ether 

 precipitated the blood proteins in the form of a green jelly and even- 

 tually, after some hours, became bright yellow with pigment. How- 

 ever, when alcohol was used as a protein precipitant, the pigments 

 dissolved at once in the supernatant alcohol, especially if absolute 

 alcohol was employed. If the affinity of carotin for blood protein, as 

 found in some cases for mammals, is a universal property of this 

 pigment, these results of Poulton's on the haemolymph of caterpillars 

 lend support to the tentative conclusion that the chief carotinoid of 

 the larvae and pupae of butterflies is carotin. 



In view of the small number of insect species studied from the point 

 of view of carotinoids it may be well to mention that the species 

 of Lepidoptera examined by Poulton were as follows: Pygaera 

 Bucephalus, P. Meticulosa, Smirinthus Tilice, S. Populi, S. Oscellatus, 



