1. Weijlard J., Tishler M., Erikson A. E., J. Am. Chem. Soc.66(1957), (1944).
2. Grumbles L. C., Delaplane J. P., Higgins T. C., Poult. Sci.27(605), (1948).
3. Long P. L., Br. Poult. Sci.25(3), (1984).
4. The data are from Agricultural Prices [U.S. Department of Agriculture National Agricultural Statistical Service (NASS) Washington DC]. Inflation correction factors to adjust the historical data to 1998 prices were listed at http://www.orst.edu/Dept/pol_sci/fac/sahr/sahr.htm a Web site maintained by Robert C. Sahr (Oregon State University) which is part of the “Resources for Economists” Web site available at http://rfe.wustl.edu/EconFAQ.html.
5. Thanks to D. Kennerson and K. Bruce of NASS for their assistance in obtaining the historical price data and to H. Geer and R. Nolan for their advice on correcting these data for inflation.