1. A method of identifying a state of health of a tissue in vivo, the method comprising the steps of: illuminating a tissue in vivo with light having a wavelength of about 337 nanometers; receiving from the tissue a response comprising fluorescent light having wavelengths of about 403 nanometers, about 414 nanometers, and about 431 nanometers; computing a first ratio, the first ratio being an intensity of the fluorescent light having a wavelength of about 403 nanometers divided by an intensity of the fluorescent light having a wavelength of about 431 nanometers; computing a second ratio, the second ratio being an intensity of the fluorescent light having a wavelength of about 414 nanometers divided by the intensity of the fluorescent light having a wavelength of about 431 nanometers; and deducing a state of health of the tissue depending on the magnitude of the first ratio and the magnitude of the second ratio to a linear discrimination function.