Full Idea
Weierstrass effectively eliminated the infinitesimalist language of his predecessors.
Gist of Idea
Weierstrass eliminated talk of infinitesimals
Source
report of Karl Weierstrass (works [1855]) by Philip Kitcher - The Nature of Mathematical Knowledge 10.6
Book Reference
Kitcher,Philip: 'The Nature of Mathematical Knowledge' [OUP 1984], p.259