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
The conception of the plan of keeping collections of mammals, birds and reptiles for exhibit is prehistoric, but the method of exhibiting animals in a park today has changed in degree as much as the mode of transportation from bullock cart to modern car.
Schroeder, C. R.
"Veterinary Medicine in a Zoological Park,"
Iowa State University Veterinarian: Vol. 1
, Article 11.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol1/iss3/11