Complex sentence: The initial Act of 1864 was passed after concern over the high levels of venereal disease in the armed forces: during the 1860s, one in three sick cases in the military was venereal in origin.
Split into simpler sentences: The initial act of 1864 was established after concerns arising over the high levels of venereal disease in the armed forces. During the 1860s, one in three sick cases in the military were venereal in origin.