NERVE ACTIVITY 



application of very special methods. But blocking a complex 

 biological function is always much easier and fundamentally 

 different from an attempt to reproduce it or to modify its various 

 aspects. We have here to deal with observations on two differ- 

 ent levels. The existence of a chemical mechanism established 

 in vitro, which satisfies all the characteristics required to be 

 responsible for the primary process and knowledge of some of its 

 properties, is one level. Testing the system organized in a special 

 structure in the intact cell is an entirely different level. 

 Between them is a tremendous gap. This is true not only for 

 the problem of nerve impulse conduction but for all those bio- 

 logical functions where knowledge has advanced to the molec- 

 ular level. Physical methods are frequently extremely sensitive. 

 They may give valuable clues on the cellular level, they may 

 raise interesting questions. They never can explain mecha- 

 nisms of living cells, which can be understood only with knowl- 

 edge of the structure and the underlying molecular processes. 

 Without an integration of the results of various types of approach 

 a satisfactory understanding of conduction is impossible. 



In 1949 Otto Warburg closed a lecture on respiration 

 presented in New York with the remark: "100 years ago 

 Claude Bernard made the statement that not a single biological 

 mechanism is really understood. What was true then seems 

 true still today." No claim has been made that the elementary 

 process of conduction is now understood, but a variety of chem- 

 ical facts have been established which have opened new ways of 

 approach to the understanding and to the investigation of the 

 mechanism of conduction. These basic biochemical facts can- 

 not be ignored. Any new progress must take into account these 

 developments just as well as the results of physical recordings and 

 the facts available concerning structure and ultrastructure. 



Perspectives 



The preceding chapter should not be interpreted as a 

 resignation to the belief: "Ignoramus, ignorabimus." In 



649 



