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
In 1928, Gragert, making an investigation of the various methods for the diagnosis of early pregnancy, came to the conclusion that, as yet, the chemical methods for the early determination of pregnancy were too inaccurate. On the other hand, the hormone test devised by Aschheim and Zondek was positive in 77 out of 78 pregnant women and positive in only three out of two hundred thirty-six non-pregnant controls.
Smith, C. L.
Iowa State University Veterinarian: Vol. 3
, Article 8.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol3/iss3/8