William Harvey (1653), a century before the discovery of oxygen demonstrated through dissection of cold- and warm-blooded animals that blood circulates through the body by the pumping action of the heart:
"It is absolutely necessary to conclude that the blood is in a state of ceaseless motion; that this the act or function which the heart performs by means of its pulse; and that is the sole and only end of the motion and contraction of the heart."
In his investigations into the origins of life and fetal development, Harvey further pointed out the meaning and importance of pulsations of the umbilical cord:
"Moreover, it is a sure way to know whether the Infant that sticketh in the birth be alive, or not, by the pulsation of the Vmbilical Arteries. But most certain it is, that those Arteries are not moved by the virtue or operation of the Mothers, but of his own proper Heart: For they keep a distinct time and pawze, from the Mothers pulse: which is easily experimented, if you lay one hand upon the Mothers wrest, and the other on the Infants Navel-string. Nay in a Casarean Section, when the Embryo's have been yet involved in the membrane called Chorion, I have oftentimes found (even when the Mother was extinct, and stiffe almost with cold) the Vmbilical Arteries beating, and the Foetus himself lusty."
Harvey, William. Anatomical exercitations concerning the generation of living creatures to which are added particular discourses of births and of conceptions, &c.London : Printed by James Young, for Octavian Pulleyn, and are to be sold at his shop at the sign of the Rose in St. Pauls Church-yard, 1653. From Early English Books Online http://eebo.chadwyck.com/.