Final pre-publication version of J.A. Schuster (2017) ‘Consuming and Appropriating Practical Mathematics and the Mixed Mathematical Fields, or Being “Influenced” by Them: The Case of the Young Descartes’ in Lesley Cormack, Stephen Walton and John Schuster (Eds.) Mathematical Practitioners and the Transformation of Natural Knowledge in Early Modern Europe, Dordrecht, Springer pp.37-65. An historiographical exercise and case study.