What St. John affirms is, that a certain invisible angel or minister--an intelligence, as we are wont to speak--was the instrument of making the water of the Pool of Bethesda beneficial to the persons who went down into it. He accounts, in this way, for its operation being more useful at one time than another. That assertion, you say, interferes with the doctrine that there were certain properties in the water itself which affected the condition of human beings. How does it interfere? You hold that the vaccine matter has in itself the property of counteracting the virus of the small-pox. But you hold also that the intelligence of Jenner had something to do with making this vaccine matter available for the actual cure of patients afflicted by the small-pox; you hold that the intelligence of different medical men has something to do with bringing the preventive power to bear on particular cases. You know this for a fact; but physical science tells you nothing of the way in which the intelligence cooperates with the natural agent. The notion that it does is an excusable fallacy; yet it is a fallacy. _In no instance whatever can the mere study of physics help you to determine anything respecting moral or intellectual forces; though at every turn the study of physics compels you to the acknowledgment of such forces._ It will save us from innumerable confusions, if we take this proposition in the length and breadth of it. Through neglect of it, the physician and the metaphysician are perpetually stumbling against each other, when they might be the greatest helpers to each other.