At the age of 14 he also began to receive training at Frederick's Hospital where chief surgeon Alexander Kølpin "accustomed his ear, heart and hand to the surgical profession".

[1] In 1769 the anatomist and botanist Christen Friis Rottbøll made the hard-working and ambitious seventeen-year-old student his prosector and later that same year he was appointed to army company surgeon.

Callisen now saw to his further education at the Theatrum Anatomico-chirurgicum and after his return to Denmark from a journey abroad in 1771 secured him a position as assistant surgeon at the søkvæsthuset.

Winsløw returned to Denmark in 1780 and succeeded Behrens as head surgeon at Frederick's Hospital the following year.

His observations during the dissection of cats and dog of respiratory movements of fetuses intra ovum enabled P. Scheels to write his thesis on this subject.

During the siege and bombardment of Copenhagen, Winsløw was responsible for organizing the lazarets and personally acted as head surgeon at one of them.

His ability to work was inhibited by increasing problems with dropsy during the lat years of his life which ultimately caused his death.