In the study in scarlet, Dr Watson informs us that it was during the Afghan campaign, when he was posted with the Northumberland Fusiliers, that his shoulder, the left one, was hit by a jezail bullet in the Battle Of Maiwand. We got lucky that he was, otherwise he might not have been discharged and become late of the Army Medical Department, thus allowing him to return to London and then meet the great detective afterwards.
However, I endeavour here to refer to an entirely different matter, which is the nature of the good doctor's injury. Watson quite often moans about the weather and we are made aware that he likes heat better than the wind and cold. On some particularly cold mornings or evenings, Watson often complains of pain in his leg....where a jezail bullet hit him. It seems that Watson is referring to the same wound, albeit in a different limb. The reference is more evident after the affair of the reichenbach falls and more so after the good doctor had lost his first wife. There is no mention of a leg wound in the adventures or the memoirs and it is the latter cases where Watson starts to mention it. If my memory serves me right, he makes a reference in the second stain and in subsequent cases.
Is it the good doctor's memory or is there something else? From his clear and lucid accounts, it is clear that Watson never hesitated to run either towards or from danger. He never complained of an impediment preventing him from doing so. Thus clearly, the injury was not in the leg.
It is also abundantly clear that Dr watson had a fascinatingly accurate memory, otherwise we would never had been able to be privy to all the conversations and the events that he has so faithfully recorded.
It seems something else is at work. Was Dr Watson merely inventing his injury? If at all he was ill in Kandahar, was it an infectious disease that Watson felt was too trivial to be announced? Did he feel that a serious injury might win him more than sympathy?
There is no doubt in my mind that Watson was quite economical when it came to mentioning his numerous encounters with the fair sex. Did he observe the same economy here too? Surely, the great detective himself never mentioned Watson's injury in his conversations nor in the two accounts that he himself wrote.
As our good doctor aged, so too his memory and perhaps in that might lie a simple explanation. Else, future students or present experts of the Canon must try to unearth fresh evidence to try to solve the case of the jezail bullet.