A few people have asked how to deal with a situation where you want to use an idea or quotation that your source quotes from a second source. This points to one of the main reasons we cite sources in the first place: so researchers like you can consult a works cited page and use that information to track down the original source. Occasionally, however, this is not possible. In one of these cases, use the MLA guidelines for citing what is called an indirect source. Our handbook does not address this, but Purdue University's Online Writing Lab (a very useful website) provides the following guidelines:
Citing Indirect Sources
Sometimes you may have to use an indirect source. An indirect source
is a source cited in another source. For such indirect quotations, use
"qtd. in" to indicate the source you actually consulted. For example:
Ravitch argues that high schools are pressured to
act as "social service centers, and they don't do that well" (qtd. in
Weisman 259).
Note that, in most cases, a responsible researcher will attempt to
find the original source, rather than citing an indirect source.