Explanatory Note 



The series embodies results of investigations., usually of 

 i*estri&ted scopej intended to aid or direct management or 

 utilization practices and as guides for administrative or 

 legislative action. It is issued in limited quantities for the 

 official use of Federal^, State or .:;ooperating agencies and in 

 prctisssed form for economy and to avoid delay in publication. 



Washingi'-on, D. 

 Marehj ^ 19'5L . 



