From Chapter 2:
A curious scene took place at Oxford in 1605 when King James visited the University. Two subjects were debated by learned dons before his Majesty, and one of them, at his own suggestion, was, "Whether the frequent use of tobacco is good for healthy men?" Among those who spoke were Doctors Ailworth, Gwyn, Gifford and Cheynell. The discussion, needless to say, being conducted in the presence of the author of the "Counterblaste to Tobacco," was not favourable to the herb. The King summed up in a speech which hopelessly begged the question while it contained plenty of strong denunciation. After his Majesty had spoken, one learned doctor, Cheynell, who is described by the recorder, Isaac Wake, the Public Orator of the University, as second to none of the doctors, had the courage to rise and, with a pipe held forth in his hand, to speak both wittily and eloquently in favour of tobacco from the medicinal point of view, praising it to the skies, says Wake, as of virtue beyond all other remedial agents. His wit pleased both the King and the whole assembly, whom it moved to laughter; but when he had finished, his Majesty made a lengthy rejoinder in which he said some curious things. He objected to the medicinal use of tobacco, and quite agreed with previous speakers that such a use must have arisen among Barbarians and Indians, who he went on to say had as much knowledge of medicine as they had of civilized customs. If, he argued, there were men whose bodies were benefited by tobacco-smoke, this did not so much redound to the credit of tobacco, as it did reflect upon the depraved condition of such men, that their bodies should have sunk to the level of those of Barbarians so as to be affected by remedies such as were effective on the bodies of Barbarians and Indians! His Majesty kindly suggested that doctors who believed in tobacco as a remedial agent should take themselves and their medicine of pollution off to join the Indians.

From Chapter 8:
The allusion in these verses to a "satiric wipe" refers to a passage in the poem entitled "Conversation," which Cowper had written in the previous year, 1781. In this passage tobacco is abused in terms which Cowper clearly felt to need modification after his personal intercourse with such a smoker as his friend Bull. In describing, in "Conversation," the manner in which a story is sometimes told, the poet says:

The pipe, with solemn interposing puff,
Makes half a sentence at a time enough;
The dozing sages drop the drowsy strain,
Then pause and puff—and speak, and pause again.
Such often, like the tube they so admire,
Important triflers! have more smoke than fire.