Iowa State University Veterinarian Records, RS 22/6/0/9, University Archives, Special Collections Department, Iowa State University, http://www.add.lib.iastate.edu/spcl/arch/rgrp/22-6-0-9.html
Since diagnosis is paramount to the solution of a poultry disease problem, the experienced practitioner realizes that he cannot rely entirely on a good case history, symptoms and lesions found at necropsy to establish a positive diagnosis in many instances. The alert veterinarian soon learns that various diseases may manifest themselves in a similar manner. In such cases a differential diagnosis is essential if subsequent treatment, control measures and eradications are to be effective.
Peterson, Harvey J.; Ramsey, F. K.; and Collier, J. R.
"Identification of Bacterial Pathogens of Poultry by Practicing Veterinarians,"
Iowa State University Veterinarian: Vol. 15
, Article 2.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol15/iss2/2