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

For every dollar you spend, you can get

0.5 pounds of grapes.

For each pound of grapes, you would need $2

Explanation: