Most notably, his merits lie in the elaboration of an early form of corpuscularianism, and above all in the invention of precision instruments meant to ascertain the homeostatic balance of the body, especially with regards to pulse frequency, temperature, and insensible perspiration. These factors were indeed measured with special instruments called pulsilogia, with thermometers (hydrolabia Sanctorii) and by means of a weighing chair, also called sella Sanctorii.
By means of his works, Santorio established the principle that physical transformations are necessarily associated with quantitative parameters, and that physicians’ subjective appreciation of the individual conditions of their patients is deceptive if not mediated by the use of precision instruments.