ASSIMILATION OF CARBON 



13 



the latter substance being formed by the action of acids upon hemoglobin. 

 Mesoporphyrin has the composition Ci6Hi 8 N 2 2 , and stands between hemato- 

 porphyrin and phylloporphyrin in oxygen content. By a further decomposition 

 of hemin these authors obtained hemo pyrrol (Ci3H 8 N), a volatile oil that turns 

 red in air and changes into urobilin, which is also obtained from bilirubin. 

 When Nentskii and Marchlewski 1 succeeded in obtaining hemopyrrol and 

 urobilin from phylloporphyrin, the relationship between chlorophyll and 

 hemoglobin was conclusively established. The atomic group common to 

 both, as in the case of the bile pigments, occurs in hemopyrrol. The following 

 diagram represents the relationship existing between these three groups of 

 substances. 



Chlorophyll Hemoglobin 



Phylloporphyrin 



Hematoporphyrin 



Hemopyrrol 

 Urobilin 



Bilirubin 



Results of this kind are exceedingly important in biochemistry, since they 

 seem to illuminate the most remote period in the evolutionary development of 

 organisms, and point to a common origin of the plant and animal worlds. Dar- 

 win's theory of the origin of species is based upon the conception of variability 

 in structure, influenced by environmental conditions in the struggle for existence. 

 But the differences between organisms lie, not only in the form and structure 

 of the various organs, but also in the chemical properties of the substances con- 

 stituting the living cells. The character of the metabolic process is dependent 

 upon the nature of the intracellular substances, and these processes, in their 

 turn, determine the configuration of the cells and their differentiation into 

 organs. In other words, the form of the cell-complexes composing the different 

 organs is determined by metabolism as this has been developed by the various 

 organs in the struggle for existence, relative to various environmental condi- 

 tions. With a change of conditions, their chemical constitution and their 

 metabolism are modified, which explains why they frequently change their 

 form also. Thus, to obtain a fundamental conception of the evolution of the 

 organic world, not only the structure but also the chemical composition of the 

 cells and the products of their metabolism must be considered. From this 

 viewpoint the work of Schunck and Marchlewski, whereby the leaf and blood 

 pigments are shown to be related chemically, though widely different as to 

 function, is of great scientific interest. 2 



1 Nencki, M., and Marchlewski, L., Zur Chemie des Chlorophylls. Abbau des Pyhllocyanins zum 

 Hamopyrrol. Ber. Deutsch. Chem. Ges. 34-^: 1687-1603. ioor. 



2 Nencki, M., Sur les rapports biologiques entre la matiere colorante des feuilles et celle du sang. Arch, 

 sci. biol. St.-Petersbourg 5: 254-260. 1897. 



