2 Sir Hans Krebs 



which co-ordinate chemical syntheses in relation to growth; 

 they see to it that the quantities synthesized are related to 

 requirements. Such "primitive" control mechanisms of lower 

 organisms are also present in higher animals ; they are, in fact, 

 the basic systems upon which the action of hormones or of the 

 nervous system is superimposed. We had in mind that this 

 conference would primarily, though not exclusively, be con- 

 cerned with these "primitive" control mechanisms. No 

 doubt references wiJl be made to hormones, but any attempt 

 to cover the hormonal field of metabolism extensively would 

 have been beyond the scope of a three-day meeting. 



We are fortunate in having at this symposium a number of 

 research workers who are prominent in our field. In view of 

 the wide experience of most of the participants I find it 

 difficult to present a suitable introduction, without being 

 either too elementary, or anticipating future speakers. What 

 I would like to attempt is to describe a few experiments 

 which illustrate the nature of the problem. 



This may be generally stated as follows. The chemical 

 systems which exhibit the phenomenon of regulation, i.e. 

 adjustment of activities with reference to a purpose, are all 

 multireaction systems. They consist of a number of relatively 

 simple reactions which can be described by ordinary chemical 

 equations, but these reactions are elaborately interlocked. 

 Interlocking in chemical systems means that individual 

 reactants take part in more than one process, often in many, 

 and to understand the nature of the control mechanism we 

 must unravel the interlocking of the individual reactions. At 

 the present stage one of the main difficulties arises from the 

 fact that the component reactions of the systems which we 

 attempt to analyse are not yet fully known. Moreover, the 

 systems are heterogeneous consisting of many phases or 

 compartments separated by specific barriers and the spatial 

 arrangements of reactants are bound to play an important 

 role in the regulation of enzymic processes. 



It is probable that regulation of metabolism operates always 

 through variations of reaction velocities: reactions are 



