Note 5 — INTRODUCTION.

Respiration is a mechanical and chemical process, and consists in alternate inhalation and exhalation, which, in consequence of the oxygen gas in the air, effects a change in the venous blood that enters the lungs from the pulmonary artery. Now as this blood is charged with carbon, to which its dark purple colour is owing, it is carried off in union with oxygen in the form of carbonic acid. Hence carbonic acid is produced in respiration and the venous blood is changed into the bright red arterial blood. A common sized man will consume about 46 thousand cubic inches of oxygen per diem; equivalent to 125 cubic feet of air, and makes about twenty respirations in a minute, or for every seven pulsations breathes twice.