Getting rid of dirt, in the opinion of most people, is a good thing. However, there is nothing fixed about attitudes to dirt. In the early 16th century, people thought that dirt on the skin was a means to block out disease, as medical opinion had it that washing off dirt with hot water could open up the skin and let ills in. A particular danger was thought to lie in public baths. By 1538, the French king had closed the bath houses in his kingdom. So did the king of England in 1546. Thus began a long time when the rich and the poor in Europe lived with dirt in a friendly way. Henry IV, King of France, was famously dirty. Upon learning that a nobleman had taken a bath, the king ordered that, to avoid the attack of disease, the nobleman should not go out. Though the belief in the merit   of dirt was long-lived, dirt has no longer been regarded as a nice neighbor ever since the 18th century. Scientifically speaking, cleaning away dirt is good to health. Clean water supply and hand washing are practical means of preventing disease. Yet, it seems that standards of cleanliness have moved beyond science since World War II. Advertisements repeatedly sell the idea: clothes need to be whiter than white, cloths ever softer, surfaces to shine. Has the hate for dirt, however, gone too far? Attitudes to dirt still differ hugely nowadays. Many first-time parents nervously try to warn their children off touching dirt, which might be responsible for the spread of disease. On the contrary, Mary Ruebush, an American immunologist  , encourages children to play in the dirt to build up a strong immune system. And the latter position is gaining some ground. What is the author's purpose in writing the passage?
To stress the role of dirt. To introduce the history of dirt. To call attention to the danger of dirt. To present the change of views on dirt.