Karl Gauss (1777-1855) discusses the meaning of integrals with complex limits and briefly examines the dependence of such integrals on the chosen path of integration.
Editors. "Gausss work on integrals". The Literary Encyclopedia. First published 01 May 2009; last revised 30 November -1.
[http://www.litencyc.com/php/stopics.php?rec=true&UID=6239, accessed 26 April 2015.]