The liver cells are seen to contain a large globule of fat which pushes the cell nucleus to one side - giving the signet-ring appearance.
The heat is sufficient to keep the resulting lead oxide fused, and the porous cupel has the property of absorbing melted lead oxide without taking up any of the metallic globule, exactly in the same way that blottingpaper will absorb water whilst it will not touch a globule of mercury.
The largest pond is as sensitive to atmospheric changes as the globule of mercury in its tube.
A metallic globule with or without an incrustation may be obtained.
It may be a gas bubble, a blood clot, a fat globule, a mass of bacteria, or other foreign body that forms somewhere else and travels through the circulatory system until it gets stuck.