Complex sentence: The principal constituent of Irish moss is a mucilaginous body, made of the polysaccharide carrageenan of which it contains about 55%; the plant also has nearly 10% of protein and about 15% of mineral matter, and is rich in iodine and sulfur.
Split into simpler sentences: The principal constituent of Irish moss is a mucilaginous body, made of the polysaccharide carrageenan of which it contains about 55%. The plant also consists of nearly 10% protein and about 15% mineral matter, and is rich in iodine and sulfur.