122 THE NATURE OF ANIMAL LIGHT 



or protein derivatives as it gives a very faint Millon 

 reaction, a good positive ninhydrin test, reddish blue m 

 color, but no biuret reaction. It precipitates with tannic 

 and phosphotungstic acids but not with picric, acetic, 

 trichloracetic, or chromic acids. The extract gives a 

 faint Molisch reaction for carbohydrates. As the evidence 

 points to the presence of some protein products in the 

 absolute alcohol extract of Cypridinee, it is possible that 

 this protein is luciferin. It should be emphasized, how- 

 ever, that the Millon reaction was very faint, although the 

 ninhydrin was quite marked and the biuret negative. 



Although luciferin is not digested by trypsin, even 

 after five days at 38° C, it does hydrolyze with mineral 

 acids after about 16 hours' boiling. Some proteins, the 

 albuminoids and racemized proteins, resist tryptic diges- 

 tion but yield to acid hydrolysis. "We know also that some 

 NH-CO linkages of proteins are broken down with great 

 difficulty by trypsin as it is difficult to obtain a tryptic 

 digest of protein which does riot give the biuret reaction, 

 and the work of Fischer and Abderhalden has shown that 

 certain artificial polypeptides are not digested by pure 

 activated pancreatic juice. 



We have, then, three possibilities: Luciferin is (1) 

 either a natural proteose not attacked by trypsin, or (2) if 

 attacked by trypsin its decomposition produists (pre- 

 sumably amino-acids) still contain the group oxidizable 

 with light production, or (3) it is not protein at all. I 

 have been unable to oxidize with light production vari- 

 ous mixtures of amino-acids (from tryptic digestion of 

 beef and casein, or the acid hydrolysis products of luci- 

 ferin itself) by means of lucif erase, and consequently am 

 led to believe that Cypridina luciferin is either a new 



