I'm searching for any information on my Great Grandfather John Christopher McDonald born c.1851 (in Liverpool, Lancashire according to 1891/1901/1911 censuses). He was a corporal (so must have been in for a few years) in the Medical Staff Corps and based in Fort Pitt, Chatham in July 1886 (when he married), the Longford Barracks in May 1888 (when a child was baptised) and the Arbour Hill Barracks, Dublin in October 1890 (another baptism). He had left the service by the 1891 census. I have no information on him at all before he married. Any help or information would be much appreciated. Thank you