Heusken departed New York in October 1855 on the , and worked closely with Harris during the negotiations for the Treaty of Amity and Commerce of 1858. Harris reported to Washington in his official reports that Heusken was kind and amiable in temper, never showing violence to the Japanese, and a universal favorite. However, in his personal diary, Harris complained that Heusken was lackadaisical, stating "I believe that Mr Heusken only remembers when to eat, drink and sleep – any other affairs rest lightly on his memory" On other occasions, Harris sought to warn Heusken about his late hours.