The two kinds of death of William Hervey.

The determining factors in congestive heart failure as well as in shock are more often extracardiac than in the heart itself. Carbon dioxide tension in the blood is as important as the oxygen tension. Carbon dioxide is a hemodynamic agent of the first magnitude. It can be quickly increased or decreased by altering the ventilation of the lungs. It is a prime factor in determining whether the circulation fails from a lack or from suffocation by an excess.