Quote 7
[Henry Baker] had foresight, but has less now than formerly, pointing to a moral retrogression, which, when taken with the decline of his fortunes, seems to indicate some evil influence, probably drink, at work upon him. This may account also for the obvious fact that his wife has ceased to love him (Carbuncle.27).
Henry Baker is only a very small part of Holmes's chain of reasoning in "The Blue Carbuncle." Still, we're struck by this bit about his "moral retrogression" and "decline of his fortunes," because these two pieces of evidence are what draw Holmes to conclude "evil influence, probably drink." In other words, the inevitable endpoint of too much drinking is an end to your fortunes. These are stories about human observation, sure, but they're also about social observation – and the moralizing that can go along with it.
Quote 8
Isa Whitney, brother of the late Elias Whitney, D.D., Principal of the Theological College of St. George's, was much addicted to opium. The habit grew upon him, as I understand, from some foolish freak when he was at college; for having read De Quincey's description of his dreams and sensations, he had drenched his tobacco with laudanum in an attempt to produce the same effects. He found, as so many more have done, that the practice is easier to attain than to get rid of, and for many years he continued to be a slave to the drug, an object of mingled horror and pity to his friends and relatives. I can see him now, with yellow, pasty face, drooping lids, and pin-point pupils, all huddled in a chair, the wreck and ruin of a noble man (Twisted.1).
(Thomas De Quincey, by the way, is the author of an extraordinary memoir called The Confessions of an English Opium Eater.) In addition to being a vivid depiction of a man ruining his life through drug use, there's something else that's neat about this passage. Why is Watson – usually such an economical narrator – starting a Holmes story with this long bit about opium addiction at all? Here's where we're reminded that Conan Doyle was a doctor: this passage reads like a PSA against drug use. And considering that the British Empire continued to run a thriving opium trade right up until 1910 , you can see why this concerned doctor was trying to scare people into not taking it. While cocaine and opium may be over-the-counter medicines while Conan Doyle was writing, he still didn't want us to think that he likes them.
Quote 9
My own complete happiness, and the home-centred interests which rise up around the man who first finds himself master of his own establishment, were sufficient to absorb all my attention, while Holmes, who loathed every form of society with his whole Bohemian soul, remained in our lodgings in Baker Street, buried among his old books, and alternating from week to week between cocaine and ambition, the drowsiness of the drug, and the fierce energy of his own keen nature (Scandal.1.2).
You can really see the difference in the acceptability of cocaine when Conan Doyle wrote these stories as opposed to now. It's so matter-of-fact that Holmes spends about half his time taking drugs to relieve his boredom, as though cocaine were the same thing as Sudoku or a good crossword puzzle. Something else that's really key about Holmes's drug use is that it signals how far outside of society (as represented by Watson's "home-centred interests") he likes to live: "his whole Bohemian soul" alternates "from week to week between cocaine and ambition."