Bubonic Plague's Relation to Microbes

Hello Everyone...
And welcome to my first blog post about Microbes!  For those of you who are just browsing around, I am doing a school project for my Specialist Sciences class in chemistry.  I will start with something interesting and gross...
But first, what are Microbes?
Microbes are micro organisms, especially bacteria that causes disease and fermentation.
Now for the gross stuff...
What did microbes have to do with the notorious 'Black Death'?
Alright, so we all know that many microbes cause diseases, but none more so than the Bubonic Plague, or the Black Death. 

Black Death is spread by the microbe yersinia pestis, invading and growing inside the bodies of rats, fleas, cats dogs, farm animals and humans.  It thrives at around 37 degrees  Celsius, the exact temperature of a healthy human body.

The way that Black Death worked was rather... gruesome.  The microbe divided inside of the flea and causes a blockage inside of it, causing the flea to get hungry.  The starving flea goes to find a human for a drink of blood, and regurgitates some of the disease back into the human bloodstream.  Inside of the human bloodstream, the bacterium is found by the immune system, which launches white blood cells to kill the virus, but instead of the virus dying, it continues to multiply inside of the white blood cell.  Eventually, the blood cell dies, and yersinia pestis floods out stronger than before.  More blood cells try to kill the virus, but the disease is powerful enough to paralyze the blood cells.

It started off with a cough and a sneeze, much like a common cold or flu, but then you start to notice large and sometimes black lesions on the skin called buboes, and in fact, hence the name Black Death.  These buboes appear in your joints, genitals, under your arms... and it's excruciatingly painful.  You are forced into bed, and the buboes get larger and start leaking out pus from inside them, and you die a slow and painful death.  In just four years, from 1347 to 1351, the plague killed more than 71 million people internationally.