gristle

Cartilage; now especially: cartilage present, as a tough substance, in meat.

When you're chewing on life's gristle Don't grumble, give a whistle And this'll help things turn out for the best[…]

But she was tired of cell culture, tired of meticulously cutting away dead tissue like gristle from a steak […]

Bone not yet hardened by age and hard work.

And it is a hard and cruel thing thus in early youth to taste beforehand the pangs which should be reserved for the stout time of manhood, when the gristle has become bone, and we stand up and fight out our lives, as a thing tried before and foreseen; for then we are veterans used to sieges and battles, and not green recruits, recoiling at the first shock of the encounter.

Look at Adam through the rest of the day, as he stands on the scaffolding with the two-feet ruler in his hand, whistling low while he considers how a difficulty about a floor-joist or a window-frame is to be overcome; or as he pushes one of the younger workmen aside and takes his place in upheaving a weight of timber, saying, "Let alone, lad! Thee'st got too much gristle i' thy bones yet"; or as he fixes his keen black eyes on the motions of a workman on the other side of the room and warns him that his distances are not right.