Complex sentence: Much of his written work dealt with the correlation between physical and mental illnesses, and with Theodor Meynert (1833-1892), he was co-founder of the quarterly psychiatric journal "Vierteljahresschrift für Psychiatrie".
Split into simpler sentences: Much of his written work dealt with the correlation between physical and mental illnesses. With Theodor Meynert (1833-1892), he was co-founder of the quarterly psychiatric journal "Vierteljahresschrift für Psychiatrie".