On the Scent with Sherlock Holmes, Part 1

 

On two occasions in the Sherlock Holmes stories do we find Holmes employing a dog to help him track a scent. But beyond those two, Holmes himself displays canine-like properties.

 

While Conan Doyle does a wonderful job exposing us to so much of the late Victorian era, there's one area that doesn't come through: smells. What were some of the scents that attracted Holmes's attention on these cases, and why were they important? It's just a Trifle.