“If you dribble something on your shirt while you’re eating,” I asked Grime, “does it make sense to dab it with saliva? As a kind of natural laundry presoak?”
“That’s an interesting thought.”
Dr. Grime carries a Tide stain pen. He does not use his own spit.
Art conservators do. “We make cotton swabs on bamboo sticks and moisten the swab in our mouths,” says Andrea Chevalier, senior paintings conservator with the Intermuseum Conservation Association. Saliva is especially helpful for fragile surfaces that solvents or water would dissolve. In 1990, a team of Portuguese conservators pitted saliva against four commonly used nonanatomical cleaning solutions. Based on its ability to clean but not damage water-gilded gold leaf and low-fired painted clay surfaces, saliva “was judged the ‘best’ cleaner.” Denatured saliva, stripped of its enzymatic powers, was also tested and proved inferior to straight spit.
For more typical cleaning jobs, painting conservators, like laundry formulators, turn to commercially produced digestive enzymes. Protease, the protein digester, is used to dissolve washes made from egg white or hide glues. (Less enlightened conservators of yore used to spread glue made from rabbit hides onto canvases to consolidate flaking paint.) Lipase, the fat digester, is used to eat through the layers of linseed oil that eighteenth-and nineteenth-century painters applied to improve light refraction and “feed the surface” of their artworks.
Chevalier volunteered that some conservators’ saliva cleans noticeably better than others’, and that this occasionally prompted speculation about how many martinis these individuals were having at lunch. In reality, there are naturally large individual differences in the chemical makeup of people’s saliva.
And in people’s flow rates. Silletti and I, for instance, chewed our cotton wads for the same amount of time. I produced .78 milliliters of stimulated saliva; she produced 1.4. She tried to reassure me. “It doesn’t say anything about how good you are or how good I am with saliva.”
“Erika, I’m a dried-up husk.”
“Don’t say that, Mary.”
Silletti excuses herself. “I want to go get some ice. The reason is that even after one minute, this will start to smell very bad.”*
While she is out, I will take this opportunity to share with you the extremely surprising findings on the topic of olfactory stimulation of saliva. The notion that food smells make your mouth water is, science says, erroneous. Science has said this over and over, most recently in 1991, at King’s College London. Ten subjects donned plastic odor-delivering face masks and nickel-sized Lashley cups. (The Lashley cup, a sort of glandular beret, fits on top of the parotid and collects its secretions.) Food odors wafted into the volunteers’ noses: vanilla, chocolate, peppermint, tomato, and beef. Only one smell, and in only one subject, caused a significant increase in salivation. Oddly, this subject was a vegetarian, and she was smelling beef. Upon questioning, the woman revealed that the smell had nauseated her. The salivation was the kind that precedes throwing up.
It is easy to criticize that study. Sitting in a lab with a plastic mask on your face and sniffing chemically synthesized odorants does not approximate the typical mealtime mouth-watering scenario. This does, though. In 1960, a bright-eyed, full-lipped young physiologist named Alexander Kerr fried up bacon and eggs in his lab at Harvard. He did so in front of three hungry volunteers, whose parotid flow was measured via a type II outflow recorder*—the Lashley cup having not yet been invented. Even here, no one salivated any more than he had before the cooking began. The subject identified as A.G. didn’t buy it. A.G. was positive he could feel his mouth “watering profusely” in the moments before he began eating. Kerr insisted that wasn’t so. He told A.G. that the feeling was an artifact caused by shifting his attention to the inside of his mouth and suddenly becoming “conscious that his mouth contains saliva.” I have seen the data, but I too find it hard to believe Dr. Kerr.
IT’S BEEN SNOWING all morning. Wet clumps of flakes flock the trunks and branches of the trees outside the lab. Silletti joins me at the window. She holds the small glass beakers that contain our fresh-from-the-centrifuge stimulated samples.
“It’s beautiful,” I am saying. Silletti agrees, but I notice she isn’t looking out the window. Is it possible she thinks I am referring to the contents of the beakers? I’d say that, yes, it is possible. You’ve never seen such clear, clean-looking spit. Stimulated saliva looks, tastes, and flows like water—it is, in fact, 99 percent water. Water with some proteins and minerals. Like water from different springs, each person’s saliva contains minerals in unique proportions. (People whose saliva naturally contains a lot of salt are slightly oblivious to it in their food.) “So somebody,” I observe, “could do a taste test with various salivas.”