David Runnion wrote,

>>If she broke a string on the instrument she probably would have had
>>to stop and either replace the string or, what's often done, grab the
>>concertmaster's instrument and finish the piece.

Richard Todd differed:

>I have to disagree.  In my student days, my A-string broke shortly after
>I began the finale of the Mozart D major (4). ...snip..it wasn't
>as hard to play in tune as you might imagine.

In an emergency, you can finish a piece perhaps especially in orchestra,
but a professional will always stop and put on a new string.  You simply
can't fly the plane with one engine flapping around on the starboard wing.
In orchestras there is a standard system for passing back instruments to
the back stand if you break a string at the beginning of the symphony,
the instrument gets passed from front to back, and instruments get passed
around so that the front players don't have to sit there without an
instrument, while one person goes offstage and changes the string..  Some
sections have a designated stringbearer who carries a full set on stage
in a pocket so they can be changed without a pit stop.  If you're sitting
in the back of the section you simply walk off and change the string.
(Sometimes, depending on the piece and the conductor, even grabbing half a
cig, and changing the string as slowly as possible.) In chamber music the
performance usually just comes to a grinding halt, the performer grins,
walks offstage and changes the string, people chat and chuckle, and when
the player returns with the instrument fully equipped, the audience claps
a little and everyone sort of smiles, and the group starts at the beginning
of the movement, usually (one hopes) to the delight of the gathered public.

Dave Runnion