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THE QUARTERLY REVIEW OF BIOLOGY 



Hoppe-Seyler who first discovered phyllo- 

 porphyrin, which definitely established 

 the blood-chlorophyll relation. 



Nencki and Zaleski obtained hemo- 

 pyrrole from hemin by reduction, while in 

 the same year Nencki and Marchlewski 

 obtained it by reduction from phyllo- 

 cyanin. From this it at once became 

 evident that the molecules of hemato- 

 porphyrin and phylloporphyrin consist of 

 the same or closely related constituent 

 parts. Willstatter and Asahina have 

 shown that the composition of hemo- 

 pyrrole is not as simple as was assumed and 

 that it consists of a mixture of pyrrole 

 homologs containing a tetra substituted 

 pyrrole and in which the trisubstituted 

 pyrroles predominate. After Hoppe- 

 Seyler chemical workers did not attempt 

 to isolate and analyze chlorophyll. Much 

 work, however, was done on the cleavage 

 products but nothing of great value was 

 discovered. Even up to the time of the 

 work of Willstatter none of the chemi- 

 cal characteristics of chlorophyll were 

 known. 



Since during all of the previous investi- 

 gations no chemical characteristics were 

 established for chlorophyll, it was not 

 possible to compare the chlorophyll of 

 different plants . Because of this situation 

 opinions differed widely regarding the 

 identity or dissimilarity of the pigments in 

 different plants . Gautier believed that the 

 chlorophyll of monocotyledonous plants 

 was different from that of dicotyledonous 

 ones. Etard in 1906 published a book in 

 which he described a long series of differ- 

 ent chlorophylls from one plant and an 

 unlimited number of chlorophylls from 

 different plants. A different chemical 

 formula was given for each of these. 

 Stokes hinted at the existence of two 

 chlorophylls, but his observations went 

 unheeded among the prominent scientists. 

 Borodin discovered crystals of chloro- 



phyll, but analysts failed to follow up his 

 investigations. Monteverde isolated the 

 crystals and determined their properties 

 spectroscopically. Willstatter and Benz 

 (1907) by working on a large scale 

 obtained crystallized chlorophyll, at a time 

 when its analysis had already been accom- 

 plished by indirect methods . Chlorophyll 

 as a pure chemical substance has been 

 known for only a few years. 



Hoppe-Seyler found that phosphorus 

 was present in chlorophyll and believed 

 that it belonged to the lecithins. His 

 hypothesis was ardently upheld by Stoklasa 

 even up to the year 1913, when he was 

 firmly convinced that potassium and 

 phosphorus are present in the chlorophyll 

 molecule. We now know that the chloro- 

 phyll molecule consists of carbon, oxygen, 

 hydrogen, nitrogen and magnesium. 



Till Willstatter isolated chlorophyll 

 just what chemical elements were present 

 in the molecule was not known with 

 certainty. Indeed, little more was known 

 than that its decomposition products 

 belonged to the pyrrole derivatives . 

 Willstatter and his coworkers first deduced 

 the characteristics of chlorophyll from a 

 consideration of the derivatives which 

 were formed by reactions with acids and 

 alkalies. At first the task appeared 

 hopeless because of the alterability and 

 chemical indifference of chlorophyll and 

 on account of the extreme solubility of the 

 pigment when diluted with so many 

 colorless and yellow admixed substances. 

 Phytol was found to make up a third of the 

 chlorophyll molecule. The "crystallized 

 chlorophyll" was found to be free of 

 phytol, while the amorphous pigment 

 contained it as a constituent of the mole- 

 cule. The results which they obtained 

 showed that chlorophyll is identical in all 

 plants and consists of two components, a 

 and b. The two components were found 

 to agree in their phytol and in their 



