Consider:
‘Why what else are you?’ returned John, looking down upon her with a smile, and giving her waist as light a squeeze as his huge hand and arm could give. ‘A dot and’—here he glanced at the baby—‘a dot and carry—I won’t say it, for fear I should spoil it; but I was very near a joke. I don’t know as ever I was nearer.’
What does 'a dot and carry' mean in this context?