Now the swelling of the muscles is so visible and sensible in the agitations of our arms and all partsofourbodies, and it is so reasonable to believe that these muscles cannot swell themselves unless some body enters them, just as a balloon cannot be blown up or become inflated unless entered by air or something else, that it seems indubitable that the nerves push the animal spirits from the brain into the muscles to inflate them and to produce in them all the movements we wish to make.