Image from the National Library of Medicine Historical Collections
Turn to these free online primary sources:
Medical Heritage Library
A consortium of medical libraries, including Yale, have put parts of their collections available online. Over 300,000 freely downloadable primary source books, many from 1780-1923. On the Medical Heritage Library website, under the Content tab, you can find primary resource sets on vaccination and disability, as well as access American and State medical society journals.
National Library of Medicine (NLM) Historical Collections
Great primary history of medicine material, including digitized books, archives, and moving images (aka movies). Also see their huge image archive, which includes posters and more!
Home to a huge variety of resources, including Moving Pictures, for free use. Not limited to history of medicine, but lots of possible primary sources here. Make sure, if you pick a source from here, that it's uploaded by a library or other institution! See, for example, the movie Medical Aspects of Nuclear Radiation (1950).
A huge online repository of freely downloadable books and journals, from a collaboration of libraries including Yale. Not limited to history of medicine, but lots of possible primary sources here.
Digital Public Library of America
This site pulls in sources and archives (like letters and diaries) from many libraries, museums, and other institutions, as well as big databases like Hathi Trust and Internet Archive. Look at the primary sources sets and exhibitions, including this one on the Atomic Bomb and the Nuclear Age.
Industry Documents Library-Tobacco, Chemical, Food, and Drug
The UCSF Industry Documents Library (IDL) is a portal to aid investigation about cross-industry corporate practices that are detrimental to public health. IDL currently brings together materials created by the tobacco, drug, food, and chemical industries. These collections are an important tool for researchers, lawyers, journalists, advocates and the general public as they expose industry tactics around marketing campaigns, regulatory strategies, and public health policy formulation.