cigarette advertisement in books

[bronte]

I was thinking about this: in many of the old paperback gothics there were cigarette advertisements in the middle of the book. Why do you think they were there? Did the cigarette companies have a agreement with the publishing house or the author's? And why only cigarette ad's and not other things, like soap or perfume or something? Now you would never ever have an advertisment in a book. Am I the only one that thinks it was practice was odd?