Full Idea
'Ten' must mean ten bodies, or ten sounds, or ten beatings of the pulse. But though numbers must be numbers of something, they may be numbers of anything.
Gist of Idea
Numbers have generalised application to entities (such as bodies or sounds)
Source
John Stuart Mill (System of Logic [1843], 2.6.2)
Book Reference
Mill,John Stuart: 'System of Logic (9th ed, 2 vols)' [Longmans, Green etc 1875], p.293
A Reaction
Mill always prefers things in close proximity, in space or time. 'I've had ten headaches in the last year'. 'There are ten reasons for doubting p'. His second point puts him very close to Aristotle in his view.