Volatiles

Here, we’ll explore the science behind the extraordinary abilities of the dogs nose.

Dogs detect odours both direct from the source and as residual odours that persist in an area long after the source has left. Odour molecules are chemicals that can be dissolved in water, and they need to be small enough to be volatile so that they can vaporise and, having reached the nose, can then be dissolved in mucus.

In the human the normal metabolic processes are altered in disease and this may result in the production of volatile organic compounds (VOCs) which diffuse into the blood stream and are then excreted in breath or in urine 5. Dogs can detect these VOCs at an incredible, tiny concentration of 0.001 parts per million 6. However it should be noted that training a dog to detect the “odour fingerprint” for a particular type of disease among the thousands of odours normally found in a sample of breath, urine, blood or faeces without recourse to the “pure source” is extremely challenging 7. In addition the dog has to learn to ignore the vast number of background odours. Thus, training a Medical Detection Dog is more complex than training a dog to detect explosives or drugs 8. 

Acknowledgements
Written and compiled by Dr G Farrer-Born
Photography by Julia Cleaver www.juliacleaver.com 

References
1. Tyson, P., and Buck, B, L., Dogs’ Dazzling Sense of Smell. 4 October 2004. Nova Science Now.
2. Horowitz, A., Inside of a Dog. 2012. Pub Simon and Schuster UK Ltd. 2. P72.
3. Press Release. The 2004 Nobel Prize in Physiology or Medicine to Richard Axel and Linda B Buck. 25 Jul 2004.
4. Craven, B, A., Paterson, E G., and Settles, G, S., The fluid dynamics of canine olfaction: unique nasal airflow patterns as an explanation of macrosmia. 6 June 2010, In: L R Soc Interface. 6;7(47):933-43. 
5. Haick, H., Broza, Y Y., Mochalski, P., Ruzsanyi, V and Amann, A., Assessment, origin and implementation of beath volatile cancer markers. 4 Dec 2013, In: Chemical Society Reviews. 7; 43 (5): P 14232-49.
6. Waggoner, L, P., Jones, W., Williams, M., Johnston, J, M., Edge C, Petrousky J A. Effects of extraneous odours on canine detection. In: DePersia AT Pennella JJ (eds) Enforcements and Securities Technologies: Proc.SPIE, vol. 3575,1998:p355-62.
7. Willis, C. M., Church, S. M., Guest, C. M., et al. Olfactory detection of human bladder cancer by dogs: proof of principle study. 23 Sep 2004, In: The British Medical Journal 329:712.
8.  Guest, C, M., The Science Behind Medical Detection Dogs. The Sniff. Spring/Summer 2014

The Dog’s Nose   Anatomy   The importance of mucus  

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