We must realize that Boyle was primarily a chemist and not a biologist. He thought in chemical terms, drawing his examples from physics and chemistry; he did not think in terms of the living creature or the organism, and as a mechanist he passed quite lightly over the concept or organismic behavior. His basic anti-Aristotelianism prevented his appreciating the biologically oriented thought of Aristotle. Instead, Boyle talked about the inorganic world, of water, of metals and elements, of physical properties. He ignored that inner drive which Spinoza called the _conatus_; or the _seeds_ of Paracelsus or van Helmont; or the persistence over a time course of any "essence" or "form." Since he dealt with phenomena relatively simple when compared with living phenomena, he could, for this very reason, make progress, up to a point. As a chemist, he could seek fairly specific and precise correlations of various concrete environmental factors, and then assume that living beings behaved as did the inorganic objects which he investigated. However, he always excepted the soul of man, as outside his investigations. But while Boyle was a skillful chemist, judged by the standards of his time, we cannot call him a skillful medical investigator. This represents, however, the fault of the era in which he lived rather than any fault peculiar to him. Boyle's medical studies fall into at least two categories. These were the purely physiological experiments, such as those on respiration or on blood, and the more clinical experiments, concerned with pharmaceuticals, clinical pharmacology, and clinical medicine. The purely physiological experiments have great merit and were profoundly influential in shaping modern physiology. The clinical experiments throw great light on the development of critical judgment in medical history, and the relations of judgment and faith. In 1775, John Hunter wrote a letter to Jenner that has become quite famous. Hunter had just thanked Jenner for an "experiment on the hedgehog." But, continued Hunter, "Why do you ask me a question by way of solving it? I think your solution is just, but why think? Why not try the experiment?"[50] The word "just," of course, in its eighteenth-century sense, means exact or proper, precise or correct. A "just solution" is one that is logically correct. The "think" refers to Hunter's own uncertainty. He is not content with a verbal or logical solution to a problem, he wants empirical demonstration. Why, he is asking, should we be content with merely a logically correct solution when we can have an experiential demonstration. _Try the experiment._ Put the logical inference to the test of experience. This empirical attitude, not at all infrequent in the latter eighteenth-century medicine, was quite unusual in the seventeenth-century medicine. This was precisely the attitude that Robert Boyle exhibited in his clinical contacts.