This is obviously... a lot... to take in, but Watson listens to it with increasing amazement. Not all of it makes perfect sense, rattled off in this haphazard way without context he lacks, but enough is clear that it sounds downright miraculous.

"I don't even know what to say," he murmurs. "I don't know where to begin. It sounds as though in my time, we are on the verge of a great many breakthroughs. My god, ten years ago I nearly died of enteric fever in Afghanistan, and it quite ruined me, and it's only in the years since that we've really confirmed that a bacillus is the cause, but with these antibiotics... It would never have been so severe."

Would he have been sent back to the front, in that case? Perhaps. He would never have met Holmes, if so.

"And the eradication of smallpox! That is the dream of variolation, and to know it will be successful is incredible. And then to turn that on other diseases, all the little things that kill so many children. We can treat diabetes? Truly?"

Not knowing what to say, Watson runs a hand over his forehead. "I can scarcely imagine, but it sounds amazing."