A analysis of the sense of smell, beginning with the nose, the olfactory epithelium and the different types of receptor proteins, and progressing through the processes of sensory transduction, transmission of neural signals to the olfactory bulb, and thence into the higher regions of the brain. I also discuss the sense of smell in humans compared to that of other animals, with a focus on the special abilities of bloodhounds. Recommended prerequisite is Episode 38: Neurons and Synapses.