One plant that he soon tasted was lobelia. He was four years old at the time, he recalls, and had gone to look for his father’s cows. While on this errand “I discovered a plant which had a singular branch and pods … and I had the curiosity to pick some of the pods and chew them ; the taste and operation produced, was so remarkable, that I never forgot it.” Later, Thomson adds, he “used to induce other boys to chew it, merely byway of sport, to see them vomit.”

But it was not until some twenty years had passed that Thomson was persuaded that lobelia, a smallish plant with pale blue blossoms, could do more than just make people sick to their stomachs. There was, and is, disagreement as to whether Thomson was the first to use lobelia as a medicine. Lobelia is also called Indian tobacco, and it was well known to the Penobscot Indians before Thomson was born, although it is not clear whether they took it as a medicine or dried its leaves and smoked them.

However that may be, Thomson’s discovery of its curative powers was made on a summer day while he was cutting hay. As he recalls the incident in the “Narrative,” he cut a sprig of lobelia and offered it to one of his fellow mowers with the suggestion that he eat it. “When we had got to the end of the piece, which was about six rods,” Thomson writes, “he said that he believed what I had given him would kill him, for he never felt so in his life. I looked at him and saw that he was in a most profuse perspiration … he trembled very much, and there was no more color in him than a corpse. I told him to go to the spring and drink some water; he attempted to go, and got as far as the wall, but was unable to get over it, and laid down on the ground and vomited several times.”

Fortunately this medical experiment ended happily. Thomson helped his companion into the house, “and in about two hours he ate a very hearty dinner, and in the afternoon was able to do a good half day’s labor. He afterwards told me that he never had any thing do him so much good in his life; his appetite was remarkably good, and he felt better than he had for a long time.”

Soon afterward Thomson discovered the virtues of steam when he was able to cure his two-year-old daughter of a disease he diagnosed as cankerrash by steaming her every two hours for a week. As word of his prowess as a healer got around, more and more people began coming to him for help, and in 1805 he gave up farming altogether and became a full-time herb doctor, treating patients in Vermont, Massachusetts, and Maine, as well as in New Hampshire. Wherever he went he ran into fierce opposition from regular physicians, one of whom, according to Thomson, tried to kill him with a scythe as he was passing by the physician’s door in Eastport, Maine. In Salisbury, Massachusetts, on the complaint of a Dr. French, Thomson was arrested for the murder of a young man named Ezra Lovett, whom he was alleged to have killed with an overdose of lobelia. For more than a month in the cold fall of 1809 he was confined to a filthy and verminous cell in the Newburyport, Massachusetts, jail, where he had no chair, no table, no fire, no candle, no bed, and only a thin and dirty blanket.

Thomson was eventually acquitted after a character witness took from the hand of the prosecutor a sample of the drug with which Thomson was said to have done the deed and ate it in open court. When Thomson had recovered from the effects of his confinement he resumed his work as a peripatetic healer, and the closing pages of the “Narrative” are richly freighted with stories of his therapeutic triumphs. To give just one example, Thomson tells of a young man who was being treated by Thomson’s enemy, Dr. French, following an accident in which three of his fingers had been cut to the bone. After three weeks, upon being advised by Dr. French that he should have the fingers amputated, the patient consulted Thomson; ten days later, with all fingers intact, he was back on his job in a nail factory. Soon afterward, when Thomson asked how his fingers were, “he said they were perfectly cured ; he wished to know what my bill was for attending him. I asked him what Dr. French had charged, and he said he had sent his bill to his mother, amounting to seventeen dollars; I told him I thought that was enough for us both, and that I should charge him nothing. His mother was a poor widow depending on her labor and that of her son for a living.”

Thomson’s robust egalitarianism was coupled with a shrewd business sense. In 1813, nine years before the publication of his New Guide to Health , he had hit on an ingenious scheme for propagating, and profiting from, his ideas. He patented his therapeutic discoveries, and began selling certificates that conferred on the purchaser “the right of preparing and using, for himself and family, the medicine and System of Practice secured to Samuel Thomson by Letters Patent from the President of the United States. …”