The Do's and Don't's of Agreeable Conversation : Page 190
This rotation of topic is not well done, however, if it is done formally, if someone says, "Now let's talk about something else for awhile" or "I think we have exhausted lawns, let's go on to gardens." This is never the mark of the best type of conversation. While if no one is really adept as a conversationalist, it may have to be done, very great care must obviously be taken so that the change will not seem to be a rebuke to the last speaker.
The best rotation is one that grows so naturally out of the stream of talk that the shift is not noticed until it is over. When it happens that way no matter how natural it seemed, it was probably guided that way by the hostess or a kindly, capable guest. In such an unobtrusive way,