Here is a link to a description of the fight:http://www.eastsideboxing.com/DempseyvsWillard.html
"Later there would be allegations of loaded gloves on the part of Dempsey, based on the words of a disgruntled member of his camp and the opinion of boxing experts, and Willard, that no man could hit so hard. It's claimed he wrapped his hands in bandages soaked in Plaster-of-Paris. The inventor of the product comes to the US to testify to the impossibility of using Plaster-of-Paris without breaking all the bones in the hands. It would be like striking a cement wall with bare hands. Doc Kearns adds fuel to the fire, and angers Willard, by joking, "Naw, I didn't use plaster of Paris on the bandages. It was cement."
A study of the film gives the explanation to the injuries. A big, overmatched fighter is hurt by the first solid punch and for three rounds plays the part of a human punching bag. The lack of a neutral corner rule allows Dempsey to hit him while he's rising or hanging on the ropes, when his body isn't prepared for the impact. Just as Houdini would die after taking an unexpected punch which ruptured his appendix, Jess Willard's body absorbs a greater degree of force than he would were he ready for the punches. The shock of impact of Dempsey's blows isn't lessened by rolling with the punch or allowing the force to push the man back, it's taken in its totality by the big body of Willard and something has to give. Bones break and teeth crumble and Jess Willard survives by the margin of minutes, perhaps only seconds, one of the worst beatings in the history of prize fighting."