“I had a new client calling, but he is overdue. By the way, Watson, you know something of racing?”
“I ought to. I pay for it with about half my wound pension.”
-- "The Adventure of Shoscombe Old Place"
In addition to being a ladies' man with experience extending across three continents, Dr. John H. Watson was a gambler. Of that there can be no doubt. In addition to his horse-racing habit, he dabbled in the stock market.
At the beginning of "The Adventure of the Dancing Men," Holmes interrupts a Watsonian reverie to observe, "So, Watson, you do not propose to invest in South African securities?" That was the conclusion of a six-step chain of deductions, but it boiled down to the fact that Watson hadn't asked for his checkbook when he went to play billiards with his friend Thurston, who was trying to talk him into buying the securities.
Can there be any real doubt that those billiard games also with Thurston involved cash on the table?
Sherlockian scholars have long speculated that Holmes, too, had a bit of a gambling penchant. Many believe that he profited handsomely from a bet on Silver Blaze. I don't know about that, but I did recently stumble upon some extra-Canonical evidence that Holmes was involved in wagering. Recently, my brother took me to a casino for lunch. And this what I saw: