What is smell?

I don’t really understand the concept of smell. So I have some questions:

Part 1: Let’s say you enter a public restroom to use the toilet. Upon entering, you notice the stink of the previous user. This stink obviously comes from the actual feces of that person. Presumably, that feces is gone, having been flushed away. So, what are you smelling?

Part 2: Since you are smelling something, that something actually has to enter your nose and interact with your olfactory nerves, right? So in the public restroom example, are actual molecules of feces entering your nose?

2a: If actual molecules of the substance being smelled are entering your nose, how come no one actually gets sick from smells? For example, I can smell rotting meat without getting sick. But if were to eat that meat, I might die.

2b: If actual molecules of the substance being smelled are NOT entering your nose, then what is entering your nose?

Part 3: Sea creatures actually smell stuff in the water. I’ve heard that sharks can smell blood miles away. Is the blood really traveling miles in all directions for a shark to smell it? If not, then what is the shark smelling?

Yes, actual molecules of the substance you are smelling enter the nose and are detected by specialized nerve endings in the olfactory organs. What makes you ill from contact with fecal matter is not so much the material itself, but rather, the microorganisms which inhabit it and very few of these become airborne. Additionally, when you smell something, it only takes a very few molecules to trigger the sense of smell, so that you can smell a dangerous substance like cyanide without actually getting ill from it.

How does the sense of smell work? What causes a smell?

As my high school biology teacher famously put it, “Yes, if you can smell somebody’s poo, it’s already inside you!

Well, I must say, I’m a little disappointed that the world actually works in this manner. I’ll be thinking about this next time I smell a stranger’s fart, or a neighbor’s bad breath, or the body odor of a bum, or maybe it’s best not to think about these things…

As should be obvious to anyone who has ever eaten beans, part of the waste matter is excreted in the form of gas. Hydrogen sulphide is the gas most responsible for bad odors, although other smelly compounds are present in fecal gases.

From here

I love the bit about gastight Mylar “pantaloons.” And when thinking about how how much your job sucks, you can comfort yourself that at least it’s better than working as a judge in a flatus odour study.

It is mostly going to be gases from the feces, rather than aerosolized solid particles of feces.

As Q.E.D. says, what would make you sick is bacteria or other pathogens in the feces. These would generally not be present in the air in enough quantity to make you sick.

See above.

Yes. Many animals can detect substances in the air or in water at extremely low concentrations. The shark is detecting blood components that have diffused through the water, and will follow the trail up the concentration gradient.

You might also consider W.C. Field’s (supposed) response when asked why he never drank water: “Fish fuck in it!” :smiley:

I’m guessing with rotten meat, you’re actually smelling product gases from the fermentation of the meat by bacteria, not the meat itself. You’re basically smelling the bacteria’s feces.

The Google ads have sunk to a new low:

Must have been that W.C. Fields quote on top of everything else. :smiley:

Not to worry. You are smelling the volatiles, like hydrogen suphide (I think), and not the molecules of the solids that make up feces.

There is a linkage between smell and taste, so if you’re smelling something, to some extent you’re also tasting it; and vice-versa.

Not necessarily. There are a lot more different kinds of smell sensors than there are kinds of taste buds (sweet, sour, bitter, salt, and MSG). You can smell airborne scents without tasting them at all; and if a compound is not volatile, you won’t smell it when tasting it.

Yes, there is minimal taste differentiation by the taste buds whereas most of taste is the job of the olfactory nerves. Ever notice how most foods taste like shit when you have a bad cold or a raging sinus infection?

I had a guidance counselor in school who told me that he lost his sense of smell in a college chemistry accident. He suffered years of depression following the incident. He lamented not being able to enjoy his favorite foods, or smell his wife’s perfume or smell the "new baby: smell of his kids. He said he would rather have been blind. Wow. The sense of smell is a powerful thing.

If smell is important to you do it while you can. You might be like me when you get old. I’ve almost entirely lost my sense of smell. Things almost have to be enough to make your eyes water before I can smell them.