Just sent an e-mail to the National Archives in Pavia to see what info they have.
In the meantime found this - don't know if it relates.
On Familysearch (the mormons):-
Argentine National Census 1895 Santa Fe, San Jeronimo.
Name: Juan Tosi b. 1865 Italy
Residence: Dept. San Jeronimo, Santa Fe, Argentina
Age : 22
Birth: 1873
Nation: Italy
Marital Stat: Soltero
Film N°: 747070
Digital Folder N°: 004160735
Looked at the actual image and the only info given is as follows:-
Alberto Tosi b. 1865 Italy
Carlos Tosi b. 1868 Italy


? Tosi b. 1873 Italy (can't make out name - does not look like Juan)
Andrea Tosi b.1875 Italy
Maria Tosi b. 1878 Italy
You can look at the actual image if you can get to a library with the film and digi numbers or online to familysearch and input Maria Giovanna Tosi b.1873 Sartirana. Parents Angelo Tosi & Maria Pasquarelli.
Maybe related to your Tosi.
Steve