A Dresser was a postion in the subordinate medical service given to persons of Eurasian or Indian birth. Trainees were generally drawn from the military orphanages.
"By 1812 there was a formal hierarchy in place whereby a pupil would advance to dresser, then to a medical apprentice, and like Surveyors, through from Third to Second, and then to Apothecary First Class" 
- Poor Relations:The Making of a Eurasian Community in British India 1773-1833 by C.J. Hawes