Complex sentence: He asked if he might keep them, but at this point the attitude of the monks changed, they realized how valuable these old leaves were, and Tischendorf was permitted to take only one-third of the whole, i.e.43 leaves.
Split into simpler sentences: He asked if he might keep them, but at this point the attitude of the monks changed. They realized how valuable these old leaves were, and Tischendorf was permitted to take only one-third of the whole, i.e.43 leaves.