76 



ADAPTATION AND DISEASE 



The Complexity of the Proteins 



But the complex protein is composed of and breaks down 

 into peptones. We can therefore represent it either as a chain 

 or a ring of linked peptone molecules, or simply as in Fig. 2, 



in which the hexagons A toF re- 

 present each a peptone nucleus 

 with its ring of glycocoll nuclei, 

 with, however, the " swinging 

 side-chains," as I have termed 

 them, indicated as in the main 

 unsatisfied, save at M, M, M, 

 and H. This represents but 

 the central skeleton of the 

 protein molecule, a frame in 

 which to place one's mental 

 picture of its nature and com- 

 plexity. Imagine that com- 

 plexity when, in the haemo- 

 globin molecule, for example, 

 there is somewhere inserted among the 700 or so carbon 

 atoms just an atom of iron and two atoms of sulphur. The 

 nuclei or radicles of which these are essential constituents 

 must have one particular place among the other nuclei 

 composing the ring or chain. Consider also the number of 

 vulnerable linkages — free-swinging side-chains that may be 

 detached by compounds in the neighbourhood having stronger 

 affinities and be replaced by others, thus altering the con- 

 stitution of the protein molecule as a whole. In the much 

 simpler bodies with which the organic chemist is in the 

 main concerned — bodies, for example, like those of the 

 benzole derivatives or the carbohydrates — we know how the 

 transfer of a given radicle from, say, the alpha to the delta 

 position upon a ring brings about profound change in the chemical 

 and physical properties of the compounds. Bodies, for example, 

 of identical molecular weight, which on analysis contain the 

 same number of atoms of carbon, hydrogen, and oxygen, and 

 on analysis afford identical radicles, mav be found to differ to a 

 remarkable degree. When two carbon atoms are united together 

 there are, or may be, six free affinities, and when these are 



