In Chapter 6 of Johnny Tremain, what warning did Mr. Quincy give Johnny?

Josiah Quincy warns Johnny not to let James Otis hear about the secret meeting about the planned tea rebellion planned for that evening.  Mr. Otis' sanity is in question, and Mr. Quincy judges that it would be better if he were left out of the proceedings.

Johnny has been sent to deliver the news about a meeting that is to be held at eight o'clock that evening.  It does not appear to be likely that the British will back down about the tea on the ships in Boston Harbor, and the Patriots are preparing to take matters into their own hands if the standoff is not resolved.  When Johnny arrives at the Quincy residence, he finds Josiah Quincy, John Adams, and James Otis sitting together, sharing port and nuts.  James Otis does not even look up when Johnny enters, and Quincy, glancing meaningfully over at "the heavy, lonely figure of Otis", puts his finger to his lips and shakes his head at Johnny.  Although Otis is a member of the group and is a brilliant man who is "passionate in his demand for the rights of Englishmen everywhere", he has shown evidence of periodic instability over the past four years.  Josiah Quincy and John Adams are watching Otis closely today.  They have concluded that his condition is not optimal, and that it would be better if he were not included in the plans this time (Chapter 6, Part 1).