"In 1925, Dr. Samuel Sheppard, at the time an emulsion scientist working for Kodak, traced impurities in photographic gelatin back to the particularities of a cow's diet. Sheppard discovered that cattle who had eaten mustard seed yielded better film speeds, because a sulfuric substance in mustard oil accentuated the light sensitivity of silver halide crystals suspended in an emulsion. Sheppard's findings suggested that the failure of Eastman's plates in 1882 had been due not to the presence of an impurity in the gelatin but rather to the absence of an impurity: mustard seed had been missing in the diets of the animals from which gelatin was rendered. The head of Kodak's research laboratory, Dr. C.E. Kenneth Mees, later recounted Sheppard's emulsion breakthrough to a lecture audience: 'Twenty years ago we found out that if cows didn't like mustard there wouldn't be any movies at all.'"
from Animal Capital by Nicole Shukin