Honey, What's this Hanging in the Refrigerator?

From Craig Schuhmann's Oregon Fishing, p. 64:

Of all the stink-bait recipes for catfish I was privy to learn about, this one stands out as the king:

Find a locker plant that will let you have a set of beef lungs with the windpipe still connected. Hang the lungs up by windpipe, then pour fresh blood into the windpipe. When the lung is full, hang in a cooler until blood coagulates (leave in the cooler for 24 hours). After 24 hours, take the lung out of the cooler and slice it into cubes. (Because of its consistency, the lung absorbs the blood.) When you put the slices on the hook, the bait will stay on the hook, but the blood will still bleed out, re-liquefying in the water.

Well, sure, everybody knows that. But where do you get the "fresh blood" to pour in the lung?