No placebo control, and not even mention of limitations of the study. Of course getting into a hyperbaric chamber with even normal pressure in itself will have a cognitive effect.
Which is a pretty shitty thing to do in my opinion.
Controls that spring to mind would be to have the chamber pressurised to a lower pressure (if you're not already familiar with hyperbaric chambers, you won't know it's at a lower pressure), or to replace the pure oxygen with normal air. Showing a dose-response relationship to pressure or oxygen concentration would go a long way towards making up for the lack of a true negative control.
Not sure if there's a lingering effect afterwards, which IIUC is what we're talking about here.
"What? Did you just scrape some cow's tits and inject fluid into a boy? No control? Where the ethics approval?"
And that's probably in the Top 10 of largest advancements in medicine of all time. Luckily he did it all before the existence of armchair keyboard warriors.
The best source concerning the Indian method of treatment of smallpox is a report by Dr. John Z. Holwell in 1767 for the College of Physicians in London. This report is an excellent source for understanding the mind of the Ayurvedic doctors of the eighteenth century. [1]
But it is known for certain that in the years following 1770, at least six people in England and Germany (Sevel, Jensen, Jesty 1774, Rendall, Plett 1791) tested successfully the possibility of using the cowpox vaccine as an immunization for smallpox in humans.
https://en.wikipedia.org/wiki/Smallpox_vaccine#Early_vaccina...