Acknowledgements

Every effort has been made to contact copyright holders. If any have been inadvertently overlooked the publishers will be pleased to make the necessary arrangements at the first opportunity.

Important: *** against any of the acknowledgements below means that the wording has been dictated by the rights holder/publisher, and cannot be changed.

Grateful acknowledgement is made to the following sources:

Figure 1: © Aleksandr Khakimullin / 123 Royalty Free

Figure 2: © Thinglass / Shutterstock

Figure 3: © Iulia Brovchenko / 123 Royalty Free

Figure 4: © YAY Media AS / Alamy Stock Photo

Figure 5a: © photografier / 123 Royalty Free

Figure 5b: © Varin Rattanaburi / 123 Royalty Free

Figure 6: © popoimagen / iStock / Getty Images Plus

Figure 7: Grant Mitchell. This file is licensed under the Creative Commons Attribution Licence http://creativecommons.org/ licenses/ by/ 3.0/ [Tip: hold Ctrl and click a link to open it in a new tab. (Hide tip)]

Figure 8: © johnkellerman / iStock / Getty Images Plus

Figure 9: University of Wisconsin