Complex sentence: From 1903--1904, he organized and conducted a parasite treatment campaign, which cured approximately 300,000 persons (one-third of the Puerto Rico population) and reduced the death rate from this anemia by 90 percent.
Split into simpler sentences: From 1903--1904, he organized and conducted a parasite treatment campaign, which cured approximately 300,000 persons (one-third of the Puerto Rico population). This work reduced the death rate from this anemia by 90 percent.