THE MECHANISM OF LIFE 483 



easily combustible, and in its combustion yields carbonic acid. 

 Thus, Pfiiiger believes that the continual taking-in of oxygen and 

 giving-out of carbonic acid on the part of living substance depends 

 upon the presence of the cyanogen radical, and that the intramo- 

 lecular oxygen is the essential condition of the tendency of living 

 substance to decompose. 



In these considerations we find a basis for an idea of the manner 

 in which the formation of a biogen molecule takes place in an 

 animal 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 non-nitrogenous decomposition-products of the living and of 

 the dead proteid, they do not appear to be of fundamental 

 importance. By the intramolecular addition of inspired oxygen 

 the biogen molecule finally arrives at the maximum of its power 

 of decomposition, so that only very slight impulses are required to 

 bring about the union of the atoms of oxygen with the carbon in 

 the cyanogen. The material of the non-nitrogenous groups of 

 atoms afforded by the explosive decomposition of the biogen 

 molecule can easily be regenerated by the residue of the biogen 

 molecule from the carbohydrates and fats that are present in the 

 living substance and contain such groups ; in fact, it has been seen 

 that these substances are consumed in the building-up of proteid. 

 " Probably this is the essential significance of these satellites of 

 the proteid molecule, " as Pfliiger very fittingly terms the 

 carbohydrates and fats. If, finally, the living substance dies, the 

 labile cyanogen-like compound of nitrogen passes over again into 

 the more stable condition of the ammonia radical with the 

 absorption of water, the nitrogen uniting with the hydrogen of the 

 water. Thus we have again the stable compounds of dead proteid, 

 such as serve for food. These are, in brief, some of the essential 

 features of the abbreviated path followed by the food in the 

 construction of the biogen molecule in the animal cell. The much 

 longer path, which in the plant cell leads from the ingestion of the 

 simplest inorganic compounds through the synthesis of the first 

 carbohydrate and on to the construction of the biogens, is for the 

 present much more obscure. 



Notwithstanding the facts that the views here developed have been 

 confirmed by experiment only in part, and that they contain many 

 large gaps, which can be filled only slowly, they afford at least a 

 basis for an understanding of the fundamental processes in living 

 substance. The metabolism of living substance, upon which all 



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