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 causes of coloration in animals is a problem that has occupied man's mind for centuries. That such is the case is certainly the result of the complexity of the problem, for it is not one which is easily solved and relegated to a place of minor importance. The color which we perceive is the net result of a myriad of inter-actions and contributing elements. Nervous control, hormones, environmental conditions such as temperature, light, and the color of the surrounding are but a few of the known factors affecting animal coloration. Perhaps the number of unknown factors far outweight these.
"Melanin Pigmentation In Animals,"
Iowa State University Veterinarian: Vol. 14
, Article 2.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol14/iss1/2