I don't think that was ever the requirement. I can't even imagine text written only in that form. There's a nearly complete lack of general understanding of what 'passive voice' means, and if you told someone to rewrite an essay to use only passive, I'm pretty sure the result would have non-passive sentences in them. (See <a href="http://languagelog.ldc.upenn.edu/nll/?p=3876" rel="nofollow">http://languagelog.ldc.upenn.edu/nll/?p=3876</a> for the failure of a recent attempt.)<p>I think the requirement was that people should not use the first person pronoun. Consider this 1968 commentary in JAMA, <a href="http://jama.ama-assn.org/content/203/4/283.extract" rel="nofollow">http://jama.ama-assn.org/content/203/4/283.extract</a> : "When a psychiatric journal published an article in which the author used the first person singular throughout, the editors apologized in a footnote for this departure from "normal" journal practice."<p>Those who didn't ignore the requirement responded by using the passive voice, as in "the temperature was measured", or circumlocutions like "the authors measured the temperature". People saw a side-effect - passive voice - and thought that that was part of the 'impersonal' writing style of science.