The following is an English translation of a description of this model taken from the 1905 Koristka catlaog:

Stand IIa, fig. 8. - Stand identical to the previous model II, except that it carries a circular rotating stage, in ebonite, with a diameter of 115 mm., And whose rotation axis can be centered on the optical axis of the microscope by means of two screws placed laterally, screws which are apposed by a spring located at the front of the stage guide. These screws also serve to give the table a shift of about 6 mm in every direction, so that the table itself functions as a translatory table. With vertical cabinet in polished mahogany wood.

F. Koristka advertisement from 1900.

This microscope was made by Francesco (Franz) Koristka (1851-1933). He was of Polish origin living in Milan. His firm, founded in the early 1880s, had a relationship with Zeiss which allowed access to some Zeiss patents. See this.

The microscope was purchased from a member of the family of the original owner who inherited it from his father, Dr. Renzo G. Olivetti (1907-1987), a physician who practiced medicine in Torino (Turin) Italy. Given the vintage of the microscope, c. 1900, it is most likely that the original owner was the grandfather, Dr. Bonaiuto Olivetti (1867-1941), who also had a medical practice in Torino. Some references by and about Dr. Bonaiuto Olivetti are available from Google books. From these references, it would seem that he specialized in gastroenterology.