Carl Zimmer

The Soul Made Flesh

As Sydenham saw patients by the hundreds, he began to see patterns. The same clusters of symptoms took a nearly identical course through different people. Galenist doctors treated a disease as the unique disturbance of an individual, but Sydenham now saw it otherwise. 'The selfsame phenomena that would be observed in the sickness of a Socrates you would observe in the sickness of a simpleton,' he declared. A wave of 'intermittent fevers,' probably a virulent strain of malaria, swept through his neighborhood in the early 1660s, and Sydenham found that no matter whom it claimed, it followed the same distinct and specific course. He found ways to distinguish other fevers, building up lists of linked symptoms that separated one disease from another. 'It is necessary that all diseases be reduced to definite and certain species, and that with the same care which we see exhibited by botanists,' he wrote. He classified diseases as if they were thistles and lilies.

Sydenham's huge practice also allowed him to gauge how well different kinds of remedies worked. He recognized that the poor sometimes overcame their illnesses without any medicine at all and that medicine even could do more harm than good. Bad medicine, Sydenham claimed, had caused more slaughter and havoc 'than hath bin made in any age by the sword of the fiercest and most bloody tyrant that the world ever produced.' Sydenham didn't know how nature healed people, but he was willing to accept his own ignorance rather than invent some ornate explanation. 'Nature by herself determines diseases, and is of herself sufficient in all things against all of them,' he declared. The best a physician could do would be 'joining hands with nature.'

He experimented with different treatments and discovered that his patients with smallpox fared better when he let them wear thin clothes and rise from bed; the traditional practice would have required keeping them warm and giving them cordials to drink. It did not bother him that he did not know exactly why his remedy seemed to work. It would make no more sense to expect a master cook to explain the chemistry of his stews.

Other physicians were outraged and tried to have his license revoked, but Sydenham would not change his medicine. 'It is my nature to think where others read, to ask less whether the world agrees with me than whether I agree with the truth; and to hold cheap the rumor and applause of the multitude.'

Locke was fascinated by Sydenham's radical medicine and began to follow him on his rounds. As he treated Lord Ashley's household, Locke began to imitate Sydenham. One night in 1668, Ashley began to vomit violently, and his skin turned rusty red. After a few weeks of paroxysms, a tumor pushed up under the skin around his liver. It was the size of an ostrich egg and yielding to the touch. Locke had Ashley's skin seared open and then had the tumor ruptured. In addition to the normal pus and blood, a baffling collection of what Locke called 'bags and skins' emerged from the incision. To let the wound drain, Locke had a silver pipe placed in Ashley's side.

To understand the bags and skins, Locke followed Sydenham's example. He polled all the physicians he knew for any similar cases they might have seen and collected tales of people who had had the same condition and recovered. (The bags and skins were actually the cysts of a tapeworm.) After gathering what evidence he could, Locke decided to leave the pipe in Ashley's side, so that he would not have to be cut open again in later years. It was a decision for which Ashley would be forever grateful to Locke, despite the nickname it supplied his political enemies: Tapski.

For Locke, Sydenham was the breathing opposite of his Oxford professors: a brash, practical healer interested only in saving lives through direct experience. Locke peppered his new friend with fundamental questions about his medical methods. Could Sydenham actually know anything about the inner causes of diseases or the workings of a healthy body? Did he even need to know in order to be a good physician? Before long, the two men's thoughts merged, like questions and answers batting around within a single skull. Sydenham would sometimes start writing an essay on medicine and Locke would finish it; Locke sometimes took dictation, editing Sydenham along the way.

Locke and Sydenham were exploring a sort of medicine very different from that of Thomas Willis, whose new London practice was attracting the rich and powerful. The diarist John Ward recorded in his journal that 'Sydenham and some others in London say of Dr. Willis that he is an ingenious man but not a good physitian, and that he does not understand the way of practice.'

Willis championed autopsies and microscopes as ways to understand how medicine worked, but Locke and Sydenham believed that these ambitions were pure folly. 'All that Anatomic can do is only show us the gross and sensible parts of the body, or the vapid and dead juices,' they declared. 'The true use of parts and their manner of operation anatomy has hitherto made very slender discoveries. Nor does it give very much hopes of any greater improvement.' Anatomy, Locke and Sydenham declared, 'will be no more able to direct a physician how to cure a disease than how to make a man.'

Willis's attempts to discover the mind by mapping the brain were even more foolish. 'The brain is the source of sense and motion,' they wrote. 'It is the storehouse of thought and memory as well. Yet no diligent contemplation of its structure will tell us how so coarse a substance (a mere pulp, and that not over-nicely wrought), should subserve so noble an end. No one, either, can determine, from the nature and structure of its parts, whether this or that faculty would be exerted.'

In Sydenham's company, Locke became convinced that all causes in medicine were beyond human understanding, that physicians could only observe symptoms and grope for cures that worked for reasons unknown and probably unknowable. When Locke discussed philosophy with his friends, a radical question occurred to him. What exactly could a person know about anything—not just medicine, but any branch of human knowledge? Could it be that a lot of debate and persecution was a needless confusion brought on because people did not understand the nature of thought itself?

One particularly rich source of confusion could be found in what Locke called 'the imperfection of words.' He once found himself in an argument over whether nervous liquor flowed in the nerves, an idea championed by Willis but doubted by others. After a while, Locke stopped the dispute and asked his friends what they actually meant by the word. 'They at first were a little surprised by the proposal,' he later wrote. Thinking about the meaning of words this way was unusual in Locke's day, but his friends quickly realized that they all agreed that some kind of 'subtle' fluid passed through the nerves. Locke showed them that all their arguing over whether it was actually a liquor, whatever that meant, was beside the point.

At some point in 1670, Locke decided that he and his friends would have to get past these simple obstacles of language and thought before they could truly understand anything. 'It was necessary to examine our own abilities,' he later wrote, 'and see what objects our understandings were or were not fitted to deal with.' Locke took on the task himself, starting an essay that he worked on from time to time, periodically producing what he referred to as 'incoherent parcels.'