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Using a canine model we have studied the relationship between the interdigestive cycle in the small intestine, motility changes in the biliary tract and bile acid output into the duodenum from direct hepatic secretion and gallbladder emptying. Under anaesthesia catheters were inserted into the gallbladder, common bile duct and duodenum, and electrodes were attached to the small intestine in five dogs. These animals were subsequently studied conscious and fasting. A double marker technique was used to measure bile acid output from the gallbladder and liver while pressure in the gallbladder and common bile duct and electrical activity in the small intestine were monitored. Four complete interdigestive cycles were recorded in each dog. Output of bile acids from the gallbladder fluctuated with the phases of the cycle: being lowest in phase I (3.9 +/- 0.7 mumol/min); increasing significantly (P less than 0.005) in phase II (9.8 +/- 1.0 mumol/min); remaining elevated in phase III (13.9 +/- 1.7 mumol/min); and falling significantly (P less than 0.05) in phase IV (8.4 +/- 1.8 mumol/min). In contrast, hepatic secretion of bile acids directly into the duodenum remained fairly constant. Intraluminal pressure in the biliary tract paralleled the fluctuation in gallbladder bile acid output, being significantly increased (P less than 0.05) in phases II and III. Periodic contraction of the gallbladder would, therefore, appear to be the principal mechanism for the phasic output of bile during fasting.

The growth of immersive technologies and media provide new ways for publics to access heritages. Extended reality experiences are the latest in a long history of media forms through which historical narratives can be told. In the creation of such experiences, many challenges emerge from the origination stages through to delivery, which bring together practitioners from disparate academic and professional fields. This article draws on the concept of usable pasts, to examine how disciplinary differences can create or mitigate tensions, and provide productive outcomes in the development of immersive experiences which take heritages out of museums and into the built environment. We mobilise Brown and Knopp (2008) approach of productive tensions and colliding epistemologies to draw attention to the constraints and opportunities of crossdisciplinary collaboration. Through our exploration of how to develop a design methodology for producing heritage-led immersive experiences we argue for the importance of understanding the philosophical approaches used by different stakeholders in the design process, highlight the importance of non-digital technologies and discuss how practical issues can produce ontological clashes.

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