... after-the-fact, and largely ineffective,chemical prophylaxis. Simple and to the point. Now consider the same sentence, taking advantage of opportunities to provide additional information and to expand ... an important device for qualifying ideas, adding additional explanatory information, or offering editorial comments that might influence the reader's understanding and acceptance of remarks. ... are repeated, the series is divided by commas. The comma stands for, in effect, the word and . The comma before the final item, before and , is often optional, but it is used here to make clear...