378. 'Attributable to service'.

On the issue of whether an injury is attributable to service, two questions must be answered: first, when did the injury occur?; secondly, what were the causes1 of its occurrence? If it existed before service, it cannot be attributable to service, but may be aggravated by it. If it occurred during service and if service was one of the causes of its occurrence then it is attributable to service; but if service was not a cause of its occurrence, it cannot be attributable to service, although it may be aggravated by service2. For the injury to be attributable to