If the streets of Dublin are the veins and arteries of Ulysses and the individual people are corpuscles with diverse functions, then the people, as a whole, are blood.
Blood flows continuously through the body in a closed system.
There is really no end and no beginning, except during creation and at the time of death. Each cell reproduces itself in such a way that blood will always be blood, no matter what its individual units may look like. In a similar manner, the Irish will always be Irish. Individuals may come and go, but the sense of Irishness lives on throughout history. Thus, the question might be raised as to whether or not the Irish of this decade are the same as the Irish of Joyce's time.