Visual excitation and blood clotting.

@article{Wald1965VisualEA,
  title={Visual excitation and blood clotting.},
  author={George Wald},
  journal={Science},
  year={1965},
  volume={150 3699},
  pages={1028-30}
}
Both processes involve extremely large amplification between the stimulus and the response. In vision it had been suggested that thismight be achieved by a chain of successive proenzyme-enzyme activations. Such a chain has now been found to underlie the mechanism of blood clotting. Methods are suggested for pursuing this comparison further.