VARIOUS THEORIES OF THE ORGANISM 15 



living proteid was believed to be connected with its great com- 

 plexity. Of course many differences of opinion existed with respect 

 to the details of the process, but the essential feature of this con- 

 ception of the organism is that Ufe consists in the building up and 

 the breaking down of proteid molecules. The energy developed 

 by living forms is the energy contained in these molecules. 



The necessity for the distinction between living and dead proteid 

 was pointed out by Pfluger ('75), and in later years Verworn ('03) 

 has developed the idea further in his " biogene hypothesis," of which 

 the essential feature is that certain complex labile proteid mole- 

 cules are the biogenes, the "producers of Ufe." These molecules 

 are not necessarily entirely decomposed in metabolism, but the 

 source of energy probably lies in certain chemical groups which 

 break down and are replaced by synthesis from the nutritive sub- 

 stances. According to this hypothesis the dynamic processes in 

 the organism are connected with the breakdown and synthesis of 

 these labile molecules. The molecule is not itself "ahve," but its 

 constitution is the basis of life and life results from the chemical 

 transformations which its lability makes possible. The "living 

 substance" is then not a substance of uniform definite molecular 

 constitution: such a substance would not be alive. It is rather a 

 substance in which some of the labile molecules are continually 

 undergoing transformation, i.e., life itself consists in chemical 

 change, not in chemical constitution. 



This theory of the organism leaves us very much in the dark on 

 many points. In the first place, most of the proteids as we know 

 them in the laboratory are relatively stable and inert chemically 

 and show no traces of the extreme lability or explosiveness which 

 the theory postulates as their most important characteristic in the 

 living organism. This difficulty was solved theoretically by assum- 

 ing that the lability is a property of living proteids only and dis- 

 appears with death. Death in fact was regarded as resulting from 

 this change from lability to stability. The proteids in vitro are 

 of course dead proteids, therefore we should not expect to find them 

 possessing the property of labihty. This assumed distinction be- 

 tween living and dead substance has the further disadvantage of 

 practically removing the "Hving substance" from the field of 



