14 PHYSIOLOGY OF NUTRITION 



According to Nentskii, 1 chlorophyll and hemoglobin arise from chromogens 

 that are protein decomposition products. A substance called tryptophan is 

 formed in protein decomposition by pancreatic juice; tryptophan is colored red 

 by bromine and is related, in its percentage composition, to hematoporphyrin 

 and the melanins. 



The decomposition products of chlorophyll can be separated, according to 

 Willstatter, 2 into two groups. Those obtained by the action of acids contain 

 no magnesium; the action of alkalies, on the other hand, results in such deriva- 

 tives as glaucophyllin, rhodophyllin, pyrrophyllin, and phyllophyllin, all of which 

 contain magnesium. If acids are allowed to act upon these latter substances, 

 new compounds without magnesium arise, which are related to hematoporphyrin; 

 in this way phylloporphyrin is obtained from phyllophyllin. The action of 

 acids upon chlorophyll itself gives plmophytin, in which the phytyl can be re- 

 placed by the ethyl group, giving ethyl phceophorbide; chlorophyllin modified by 

 the action of acid is designated as phaeophorbide, and phaeophytin may thus 

 be termed phytyl-phaeophorbide. 



Among the other transformation products of chlorophyll, protophyllin de- 

 serves attention; Timiriazev 3 obtained this by the action of nascent hydrogen. 

 It is yellow or red in solution, according to the concentration. It is very easily 

 oxidized, going over into chlorophyll; for this reason it must be preserved under 

 carbon dioxide or hydrogen in sealed tubes. It is stable in hydrogen, in light 

 as well as in darkness, but in carbon dioxide it is stable only in darkness; in 

 light, with carbon dioxide, it becomes green and is transformed into chlorophyll. 

 It must be supposed that carbon dioxide is decomposed in this case and that 

 oxygen is liberated, at the expense of which the transformation and greening of 

 the protophyllin occurs. Absorption bands in the orange and green regions of 

 the spectrum, corresponding to bands II and IV of chlorophyll, are character- 

 istic of protophyllin. 



It appears from many investigations that the formation of chlorophyll in 

 plants is a very complicated process. Until the publication of the work of 

 Liro 4 most authors failed to distinguish between the beginning of chlorophyll 

 formation and the visible accumulation of this pigment in plants as they become 

 green. This distinction is quite necessary. 



We shall first turn our attention to the conditions requisite for the formation 

 of chlorophyll. Light may be mentioned as the first of these. Leaves of angio- 

 sperms grown in darkness are always yellow, but such etiolated plants soon turn 



i Nencki, M., Ueber die biologischen Beziehungen des Blatt- und des Blutfarbstoffes. Ber. Deutsch. 

 Chem. Ges. 29IU : 2877-2883. 1896. 



2 Willstatter, Richard, and Pfannenstiel, Adolf, Ueber Rhodophyllin. Liebig's Ann. Chem. u. Pharm. 

 358: 205-265. 1908. Willstatter and Fritzsche, 1909. [See note 2, p. 11.] Willstatter and Hocheder, 

 1907. [See note 2, p. 8.] Willstatter, Richard, and Stoll, Srthur, Spaltung und Bildung von Chlorophyll. 

 Liebig's Ann. Chem. u. Pharm. 380: 148-154. 191 1. Willstatter, Richard, and Isler, Max., Vergleichende 

 Untersuchung des Chlorophylls verschiedener Pflanzen. III. Ibid. 380: 154-176. 1911. [The whole 

 series of studies is summarized by Willstatter and Stoll, 1913- (See note 6, p. 7.)] 



3 Timiriazeff, C, La chlorophylle et la reduction de l'acide carbonique par les vegetaux. Compt. 

 rend. Paris 102: 686-689. 1886. Idem, La protophylline dans les plantes etiolees. Ibid. 109: 414-416. 

 1889. Idem, La protophylline naturelle et la protophylline artificielle. Ibid. 120: 467-470. 1895. 



4 Liro, J. Ivar, Ueber die photochemische Chlorophyllbildung bei den Phanerogamen. Ann. Acad. 

 Sci. Fennicse (Helsinki) Ai : 1-147. 1909. 



