How do I cite a reference within an article that has been referenced?
You are talking about citing a secondary source.
What is a secondary source?
A secondary source is a citation or reference you discovered in a book, article, or other item that discusses information found in an orginal source.
Jacobson describes nursing theories .... (as cited in Nihart, 1999).
Use sparingly!! Secondary sources should only be used when the original source (or primary source) cannot be located. The original work should be named in the body of your paper. In parentheses begin with "as cited in". Then, add the last name of the author of the secondary source followed by the year of publication. Be sure to include a comma between the author's name and the publication date. End with a period if at the end of a sentence.
More Information: See page 178 in the APA 6th edition for further explanation.