Friday 13th May 2016

Following on from last year's experiment where I compared the cleanliness of the dog's feet versus my own, I thought we'd have a rematch with our tongues.

Here we see the subjects waiting for the cultures to grow - the petri dishes are pictured in the middle of the photograph, growing in our temperature-controlled laboratory environment. Highly scientific.

The big improvement this time is that I bought the right kind of agar. Last year I bought plain agar powder, this time I bought nutrient agar - the clue is in the name!



My hypothesis is that my dog's saliva kills more bacteria than my own.

Old wives tales abound regarding dog saliva, and studies have confirmed its antimicrobial properties against some kinds of bacteria. As the French saying goes, Langue de chien, c'est langue de médecin, although I don't think I'd want a doctor's tongue in my wounds either.

Conversely, human saliva contains a wide variety of bacteria which are harmless in the mouth but can be a serious risk in open wounds. People say that a bite from a human is the worst for infections, although maybe I'll try that one another time.



I made up a batch of nutrient agar plates and placed them in the fridge to set. I avoided washing my hands for 18 hours to get a good build up of microbes, and then gently pressed the fingers of my left hand into one plate, and my right hand into another plate. These were labelled as Before plates.

I held my left hand out for Stanley, who licked it for about ten seconds. I pressed my left hand into another plate, labelled After. I then licked my right hand for about the same amount of time, trying to mimic the dog's style and technique, although it was noted this his tongue is much more raspy. I pressed my right hand into a final plate labelled After.

The petri dishes were sealed and grown on a radiator in a warm room for four days.



Left hand - dog

The amount of green fungal spores visible is definitely reduced in the After plate, but there is more of the yellow (bacterial?) growth visible.


Right hand - human

The amount of green fungal spores may be slightly reduced, but not as much as the dog plate. There is also more yellow (bacterial?) growth visible.



We can see that dog saliva is better at killing some kinds of fungus than human saliva, but there are some kinds of microbes that neither saliva inhibits. More research is needed into this phenomenon before dogs can be prescribed on the NHS for wound cleaning.



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