EXPLANATORY NOTE 



Tho series embodies results of investigations, usually of 



. ^.H^codI int-'nded to aid or direct management or 



'!'■'■ tlorac'tiiesond as auides for administrative or 



°;i'iSed w'or «cno4 ond ."^o o^oid de^,:n publicCicn. 



Vashingtcn, D. C. 

 January 1951 



