Darwin recounts that one day, Brown told him personally that he challenged Cullen on " the incomprehensible ideas of atony and spasm existing in the same vessels of the body at the same time " and " thereby provoked him to manifest signs of impatience and displeasure " the result being a " coolness " that " increased at last & to rooted aversion and deep opposition . " But it was this resistance from Cullen and irritation of mind that it provoked that is, according to Darwin, " to be ascribed no small portion of that resolution and energy with which he laboured out a System of Medical Philosophy, which, though not free from errors, borrows, however, none from Cullen ."
