Can someone explain what dickens meant by this quote?

"it is a fair, even-handed, noble adjustment of things, that while there is infection in disease and sorrow, there is nothing in the world so irresistibly contagious as laughter and good humour."

I think that Dickens meant to show that the world cant hide from laughter or good humour. If you see someone laughing you tend to laugh too. If you heart a funny joke you laugh at it. This world isnt just filled with nasty its also filled with fun. 
Hope this helps but this is what i feel Dickens meant. the person grading your work may feel different

Ceuphemism hope it