Complex sentence: Treatment by fresh food, particularly citrus fruit, was periodically implemented, as it had been since antiquity, but the ultimate cause of scurvy was not known until 1932, and treatment was inconsistent, with many ineffective treatments used into the 20th century.
Split into simpler sentences: Treatment by fresh food, particularly citrus fruit, was periodically implemented, as it had been since antiquity. However until the 1930s, treatment was inconsistent, with many ineffective treatments used into the 20th century.