The Crawling Chaos himself dropped me a pointer to a fantastic resource for all sorts of vintage medical equipment and ephemera.
"Tucked away on the London Science Museum website is the History of Medicine objects collection, which contains a veritable trove of medical artifacts from throughout history. The collection includes various medical devices, advertisements, posters, drug boxes and bottles, certificates, samples... and so on. Though the collection consists mainly of items from the UK, and contains not an insignificant number of objects from outside the early 20th century, it is nonetheless an amazing and inspirational photo archive."
If anything, his description of the voluminous gallery of artifacts understates how incredible it is. The pictures below are just a small sample of the thousands on display, ranging from period medicines to the state of the art in medical technology. As with so many of the great web archives, you can literally spend hours browsing around from section to section. It's an invaluable resource for prop research, but I also found myself thinking what kind of Mythos stories the objects themselves could help tell.
A vintage blood transfusion notice. What if the donor was also passing along something more ominous than blood with each donation?
A classic patent medicine advertisement. What if the ingredients included extracts from certain alkaline herbs found on the Plateau of Leng?
A vintage nursing certificate. I've seen enough Hammer horror films to know the potential dangers of English nurses dressed in starched uniforms.
Dosage ampules for a compound used to treat "Nervous Debility". Sweet Jebus, they're already marked "POISON"!
A tin of amyl nitrate inhalers. One part of me is thinking they'd make nifty additions to a Miskatonic University expedition display. Another part remembers my dissolute youth and shudders.