Catch-em-alive O

Posted by Blackbird on April 28, 2005

What does the phrase mean?

In 'Little Dorrit', Charles Dickens said:

There were views, like and unlike, of a multitude of places; and there was one little picture-room devoted to a few of the regular sticky old Saints, with sinews like whipcord, hair like Neptune's, wrinkles
like tattooing, and such coats of varnish that every holy personage served for a fly-trap, and became what is now called in the vulgar tongue a Catch-em-alive O.

Why it's 'vulgar'? Last question, when is the first use of 'Catch-em-alive O'?

Thank you.