they don’t get attracted to it. they flow through the blood and when they reach the brain they stick there. Bacteria may present some chemotaxis, but only once they reach the brain (the brain is big if you’re a bacterium, and most bacteria have some favorite spots)
On that note, this month’s issue of Nature shows that prions move from one cell to another through the newly discovered tunnelling nanotubes. if anyone is interested in that kinda stuff, you might wanna look into that.
plasmodesmata11, you should note that cell biology is very far from being understood, even in the big picture. There are many many questions that people simply have no idea about. For example, what happens to the Golgi apparatus at mitosis? Or how can a cell direct components to the daughter cells asymmetrically in mitosis? And aside from questions regarding stuff that happens and we don’t understand, there are things which don’t even know about, like tunnelling nanotubes.
by the way, on the topic of unanswered questions in cell biology. in one of my classes I recently came across this paper http://jcb.rupress.org/cgi/content/abstract/183/5/949 as we are studying cell migration. I consider this paper to be very important for the point I was trying to make above: it basically tells us that we still have a whole bunch to learn about the cytoskeleton and how microtubule position is regulated, about vesicle targeting with clathrin coat proteins and about the transport pathways within the endomembrane system.