I have no problem getting old copies of the Philosophical Transactions of the Royal Society. I open a browser windows, type "jstor.org" and I'm pretty much there. I can browse down to the individual articles of Volume 27. Within seconds I can have a copy of Jean Denis's "Letter concerning a new way of curing sundry diseased by transfusion."
The scientists of the day had a very different problem. Hevelius, a member of the Royal Society, recieved numbers 16 to 49 from Oldenburg in August of 1669. Oldenburg could not, however, secure number 27: it was the best seller of the day. Apparently even Christian Huygens couldn't get a copy even after his father travelled to London. Hevelius and Huygens both wrote frequent letters to Oldenburg in an attempt to procure these rare numbers and complete their collections.
And now, all I have to do is open a browser window. It seems that the practice of research has become something very different from what it was.
Source: Rostenberg, L. (1989) The library of Robert Hooke: The scientific book trade of restoration England. Madoc Press, Santa Monica CA. Page 109.