LECTURE XXIV. 

 BLOOD AND LYMPH. 



IN discussing the respiratory exchange, we called attention to the 

 important part played by the red blood-corpuscles in this process ; namely, 

 their significance in the transportation of oxygen. We mentioned the 

 important fact that it is not the entire red corpuscle which combines with 

 the oxygen, but that this power is limited to the pigment contained in it, 

 which is known as hemoglobin. This substance is not a simple compound. 

 It consists of two components, which, according to their chemical nature, 

 belong to two entirely distinct classes. One of these components, globin, 

 is a protein. On account of the relatively large proportion of bases which 

 it contains, and especially of histidine, it is classed with the histones. We 

 have already mentioned that this classification is to be regarded as a 

 temporary one. Globin contains the same constituents as are usually 

 present in proteins. 1 The other component, which may be separated 

 fairly easily from the globin, contains iron and is designated as hemochro- 

 mogen. In the presence of oxygen the latter is readily oxidized to hematin. 

 In spite of a great deal of careful investigation, our knowledge concerning 

 the nature of the combination between globin and hemochromogen is still 

 very incomplete. We merely know that about 4 per cent of hemochromogen 

 can be obtained from hemoglobin. 2 It is still unsettled whether we are 

 justified in assuming that one molecule of globin unites with one molecule 

 of the iron-containing constituent, or whether several molecules of globin 

 are in combination with a single molecule of hemochromogen. There is 

 in fact no absolute proof at hand that even globin itself is a simple 

 substance. We are emphasizing these uncertainties, which in part 

 have been mentioned elsewhere, because hemoglobin has been usually 

 chosen as a foundation for the calculation of the molecular weights of 

 proteins. 



When oxygen combines with hemoglobin, oxyhemoglobin is formed, and 

 this compound crystallizes readily. From squirrels it crystallizes in six- 

 sided plates of the hexagonal system, while that from other animal species 

 crystallizes in needles, prisms, tetrahedrons or plates of the orthorhombic 

 system. The solubility of the oxyhemoglobins from different species of 

 animals is widely different. That from dogs, for example, is less soluble 



1 Abderhalden: Z. physiol. Chem. 37, 484 (1903). 

 3 F. N. Schulz: ibid. 24, 449 (1898). 



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