{The violin-soloist usually asks the concertmaster to exchange violins when
a string breaks...}

Janos Gereben wrote:

>>...  But why should it be the concertmaster who is taken out of action
>>like this? Isn't he the most indispensable member of the section?)

Deryk Barker guesses:

>Could it be that when the tradition began he was the only person with
>a reliably good violin?

The concertmaster is closest.  I watched a very silly concert once at the
university down the street.  The soloist exchanged instruments with the
concertmaster, who then passed it to his assistant concertmaster, who
passed it to the principl second, exchanging instruments each time ...
and so it went back to the last stand of second violins.  The last fiddle
player replaced the string, sent it back, and they once again did the
exchange.  The music kept playing, the soloist kept sawing away on her
borrowed instrument, till she paused, and then each instrument was in its
rightful owner's posession.  It was one of the funniest musical evenings
I've ever experienced.  Poor Bartok!

Mimi Ezust