CHAP, vii The Problem of Nutrition 417 



labile complexes, and are easily worked upon by external 

 stimulation, and that life depends directly upon their exis- 

 tence. He held that the two facts, that living substance 

 demands these labile complexes and that proteins stand at 

 the centre of life, show that living substance must contain 

 certain proteins much more unstable than those which 

 occur in dead substance ; that these are present in life only 

 and terminate life with their decomposition. Verworn said 

 further that certain proteins or protein compounds of living 

 substance are continually undergoing spontaneous decom- 

 position, even when the living substance is under wholly 

 normal conditions, while all dead proteins are able to exist 

 for an extraordinarily long time if protected from bacteria. 

 He called this labile protein biogen. 



Verworn's views differed but slightly from Pfliiger's. He 

 held that the change in the association of the nitrogen 

 with the carbon marks the construction of the biogen 

 rather than incorporation into the general living proto- 

 plasm. To quote his own words : 



' In these considerations we find a basis for an idea of 

 the manner in which the formation of a biogen molecule 

 takes place in a cell out of the ingested food. By the 

 co-operation of the biogens already present, the atoms of 

 the dead proteid molecule introduced in the food undergo 

 in the cell a rearrangement, in such a manner that an 

 atom of nitrogen always unites with an atom of carbon 

 to form the cyanogen radical with the loss of water. The 

 changes that necessarily appear at the same time in the 

 other groups of the proteid molecule are for the present 

 wholly unknown, but if we may judge from the essential 

 agreement in the nitrogenous decomposition-products of 

 the living and the dead proteid, they do not appear to be 

 of fundamental importance ' (General Physiol., Eng. ed., 

 1899, p. 483). 



A view of a different character was advanced by Sachs 

 in 1880 and 1882, and somewhat modified ten years later. 



GREEN D 



