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
A three-year-old wire haired terrier bitch was acquired with the history of never having had a normal estrum. Estrum had been manifested by a slight swelling of the vulva for three days at regular six month intervals, but no sex desire was manifested. There was no vaginal discharge, and all symptoms of estrum disappeared at the end of the third day. Coitus was refused.
White, J. Brown
Iowa State University Veterinarian: Vol. 4
, Article 7.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol4/iss2/7