566 LECTURE XXIV. 



on the contrary, that chlorophyll participates in the metabolism of 

 plants, and especially in the assimilation processes, in a way that finds 

 no analogy in the case of the pigment of the blood. We may say, 

 however, that a comparison of the disintegration products of chloro- 

 phyll with those of hematin, or, better, with those of hematoporphyrin, 

 shows considerable similarity between these apparently unlike substances. 

 And yet we cannot rightly draw any conclusions from this agreement as 

 to the biological uniformity of the pigment of the blood and that of green 

 leaves. Chlorophyll contains no iron, while in the case of hematin its 

 functional individuality apparently depends upon the presence of this 

 element. It is far more fitting to conclude that the close relationship 

 between chlorophyll and hematin, or its iron-free decomposition product 

 hematoporphyrin, is explained by the fact that hematin is formed from 

 chlorophyll. Unfortunately, no one has been able to prove positively 

 that chlorophyll is actually the mother-substance of hematin. Chlorophyll 

 is unquestionably transformed to a considerable extent while in the ali- 

 mentary canal; 1 apparently various decomposition products are formed. 

 It is not impossible that the animal organism may make use of these 

 products for the synthesis of hematin. We make this suggestion because 

 again and again we are forced to admit that the animal organism is greatly 

 dependent upon the synthetical work of the vegetable kingdom. To be 

 sure, the animal cells are capable of effecting complicated synthesis, but 

 they require for this purpose building material which has already been 

 well worked over. The plant cells are capable of producing such material 

 from the elements. Now hematin is a compound of highly complicated 

 structure. It is then hardly probable that the animal organism, which 

 in every other case makes use when possible of the building stones fur- 

 nished by the vegetable kingdom for accomplishing its synthesis, leaves 

 this material available for the construction of hemochromogen actually 

 untouched, and instead effects the complicated synthesis of hematin from 

 the very simplest material. Here unquestionably is a great gap in .our 

 present knowledge, a gap which has resulted from the attempt to decide 

 the question whether inorganic iron compounds or only organic ones can 

 be utilized by the animal cells for the synthesis of hematin. We have 

 already shown what a subordinate position is taken by the iron assimila- 

 tion compared to the formation of the complicated hematin molecule. 

 We cannot yet decide this question, but desire to leave the impression 

 that it is by no means improbable that the herbivora obtain in the chlo- 

 rophyll of their fodder the building material for that component of hematin 

 which contains the iron; and that the carnivora also utilize the color- 

 principle of the blood which is contained in their food for the formation of 

 their own hemochromogen, perhaps, to be sure, only after the hematin in 



1 Cf. L. Marchlewski: Z. physiol. Chem. 41, 33 (1904). 



