HAECKELANDPFLUGER 83 



fact that, when living substances decompose spontaneously, 

 carbon dioxide is always formed, whereas carbon dioxide 

 cannot be formed by direct oxidation of the carbon atoms of 

 proteins. The products obtained by the decomposition of 

 ' dead ' proteins and even ' dead ' proteins themselves are 

 quite incapable of this sort of oxidation. Consequently there 

 must be present in ' living ' proteins some special atomic 

 grotipings or radicals which can break themselves down and 

 oxidise themselves. 



Pfliiger considered that cyanogen represented such a radi- 

 cal in the molecule of ' living ' protein. He considered this 

 to be thoroughly demonstrated by a comparison between the 

 nitrogen-containing products of the decomposition of protein 

 obtained as a result of the normal metabolism of living organ- 

 isms with the corresponding products of the decomposition 

 of ' dead ' protein which are formed when it is broken down 

 artificially. There is a radical difference between such pro- 

 ducts. The products which are characteristic of the break- 

 down of ' living ' protein in the organism such as urea, uric 

 acid, etc., are never obtained from the artificial breakdown 

 of ' dead ' protein. Ho'^vever, these characteristic substances 

 can easily be produced from compounds containing cyanogen 

 groups by rearrangement of the elements, as occurred in 

 the synthesis of urea from ammonitim cyanate by Wohler. 

 Pfliiger thus tried to relate the whole metabolism and all 

 the properties of living protoplasm to the presence of definite 

 chemical groupings, the cyanogen radicals, entering into the 

 composition of ' living ' proteins. 



Contemporary biochemistry has long ago disproved these 

 hypotheses of Pfliiger. It has not succeeded in discovering 

 any specific cyanogen-containing radicals which differentiate 

 ' living ' from ' dead ' protein, and even the separation of 

 proteins into these two categories is now considered to be 

 without any real justification. In particular, it has now been 

 shown that the so-called reserve proteins of the seeds of 

 plants have an enzymic activity similar to that of the proteins 

 of protoplasm." The end products of nitrogen metabolism 

 in animals, urea and uric acid, arise as a result of secondary 

 synthesis and not by direct oxidation of cyanogen-containing 

 radicals in the molecules of the ' living ' protein. It is now 



