Those M&D words: Veins and Reins

[Ya Sam]

It looks like some idiom, but even google gives just one instance which 
explains nothing.

'Meanwhile, Mason and Dixon, a-jangle thro' Veins and Reins with Caffeous 
Humors, impatient themselves to speak, are launch'd upon the choppy Day, 
attending, with what Civility they may summon, the often reckless Monologues 
of others.'

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