"This kills me. John doesn't break down until Sherlock isn't there to see. I can't help but be angry with Sherlock, though. He should be there to catch John. The man deserves a hug here." John Watson, Sherlock, The Great Game
in Conan Doyle's canon, Holmes discovers a new test to confirm the presence of blood in the crime scenes. it's the experiment he is doing when he meets Watson at Bart's, and he talks about it non-stop, like a child at Christmas.