At the same time, however, the conception of radicals could not be entirely displaced, for the researches of Liebig and Welder, and those made subsequently by Bunsen, demonstrated beyond all doubt the advantages which would accrue from their correct recognition.
Ultraviolet radiation such as that which occurs with a welder's flash or use of a sunlamp, can also cause an abrasion, as well as misuse and mishandling of contact lenses.