What is the central idea developed in Chapter 4 of wheels of change: how woman rode the bicycle to freedom?

On the mode of communication of cholera" was a scientific text written by dr. john snow in 1855 about the disease cholera. what are the two primary purposes of this text? to persuade officials and citizens to be more conscious about sanitation to inform readers about new ideas about the disease using scientific evidence as support to narrate the consequences of contracting the disease to describe the lack of sanitation at the time of the story