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 the late 1600's, Christian Huggins evolved the wave theory of light, which gives an explanation of the laws of reflection and refraction, or bending. These theories have been put to use to implement the physical transmission of light through glass fibers, which depends on internal reflection. The first practical application and patent of an instrument transmitting light through glass fiber bundles occurred in England in 1928. Since then, a wide range of instrumentation has evolved for endoscopy, the visualization of internal anatomical structures through natural or surgically acquired body orifices.
"Endoscopy in the Equine,"
Iowa State University Veterinarian: Vol. 41
, Article 4.
Available at: http://lib.dr.iastate.edu/iowastate_veterinarian/vol41/iss2/4