[Letter from the Texas State Department of Health to B. L. Nelson & Associates, Inc., August 17, 1970], letter, August 17, 1970; (https://texashistory.unt.edu/ark:/67531/metapth744099/m1/1/: accessed May 21, 2024), University of North Texas Libraries, The Portal to Texas History, texashistory.unt.edu; .