I thought Missouri was the show me state. First of all, I am somewhat perplexed by that video as it seems a bit unfamiliar as to what I would expect to see.
Now, Although white blood cells do not have olfactory functions, lets say they do for this discussion. The WBC is triggered by chemo receptors, these receptors trigger a response in the cell. The cell now seeks the chemical based on a concentration gradient. It searches left, then right, then center, the cell then knows the strongest gradient and follows this path (Don't ask me how this work because I don't know). The cell continues on the strongest gradient path sniffing all the while until the unwanted organism is eliminated. The biochemistry involved is beyond me, and if this explantion is not satisfactory for you, then I suggest you do a bit of reading.