Cells isolated from trypsin-treated brain contain trypsin.

@article{Guarnieri1976CellsIF,
  title={Cells isolated from trypsin-treated brain contain trypsin.},
  author={Michael Guarnieri and Stephen Roy Cohen and EdwardI. Ginns},
  journal={Journal of neurochemistry},
  year={1976},
  volume={26 1},
  pages={
          41-4
        }
}