In the course of human events, there is perhaps no other epidemic that changed the world like "The Black Death". An inflammatory swelling of a lymph gland, especially in the groin, is called a "bubo". Being a predominate feature of this epidemic, it came to be called "bubonic plague", and changed the existence of mankind on the surface of this earth.
This plague arrived in central Europe just about the middle of "The Hundred Years War". [See last post of 8/14/14.] The book above is a good overview and summary of this event. In his preface Ziegler states:
"...no one would to-day deny that the Black Death was of the greatest economic and social importance as well as hideously dramatic in it progress."
Well illustrated [many color plates included], it presents 17 chapters on various topics beginning with "Origins and Nature" and ending with "The Effects on the Church and Man's Mind". For my own family tree climbing chapter 12, "The Welsh Borders, Wales, Ireland, and Scotland", was helpful.
The book was first published in 1969, and reprinted 1993 by Alan Sutton Publishing, Inc., Dover, NH.
Yersinia pestis was the bug. It was transmitted by infective fleas of rodents or other mammals; and/or direct contact with infected mammals or their products; and/or inhalation of contaminated airborne droplets. Rats you might say!