Extra glands

 From Path to Power by Robert Caro.

Rowe and Corcoran, disciples of Justice Holmes, called the tirelessness and enthusiasm that they admired "energy. "Holmes used to say that in the last analysis the only thing that mattered was energy, " Corcoran says, "and Lyndon just bristled with it." Fortas, more precise, says, "It was a matter of intensity more than anything, an intense concentration on whatever was being talked about, or on whatever was the problem in hand."... "The guy's just got extra glands."  [Rowe said] "Listen, I mean I worked for Roosevelt and Holmes. They were the two perfect people.  Johnson was never going to [become one of my idols] -- he and I were of an age -- but he didn't bore me for one minute. He never bored anyone.  He was a magnetic man physically, and you never knew what was going to happen next. He was a remarkable man."

...

And in describing Lyndon Johnson, the words the members of this little group use are "vibrancy," "vitality," "urgency," "intensity," "energy," -- and "passion."