Foreword 



The original literature in the field of physiology 

 has become so vast and is growing so rapidlv that 

 the retrieval, correlation and evaluation of knowledge 

 has become with each passing year a more complex 

 and pressing problem. Compounding the difficulties 

 has been the inevitable trend toward fragmentation 

 into smaller and smaller compartments, both of 

 knowledge and of research skills. This trend is not 

 only inevitable, but it is necessary to healthy growth. 

 It must, however, be accompanied by the develop- 

 ment of mechanisms for convenient and reliable re- 

 integration in order that knowledge shall not be lost 

 and research efTort wasted. 



The American Physiological Society has enlisted 

 the cooperation of physiological scientists over the 

 world in attempting to provide a mechanism in this 

 Handbook of Physiology series for providing a com- 

 prehensive but critical presentation of the state 

 of knowledge in the various fields of functional 

 biology. It is intended to cover the physiological 

 sciences in their entirety once in about ten years, 

 and to repeat the process periodically thereafter. 



Board of Publication Trustees 

 MAURICE B. visscHER, Chairman 



W I L L I .^ M F. H .^ M I L T O N 

 PHILIP BARD 



