372 PHYSIOLOGY CHAP. 



the significance of respiration lay in the renewal of the pulmonary 

 air and not in the alternate expansion and contraction of the 

 lungs, as was believed by certain iatro-mechanicians. 



The ancients were undoubtedly aware of the difference in 

 colour between arterial and venous blood. It was perhaps owing 

 to this difference that they termed the pulmonary artery vein, and 

 the pulmonary veins arteries. It was also known to the older 

 surgeons that the clot formed from the blood extracted by bleeding 

 exhibits the scarlet colour of arterial blood in the upper layers, and 

 the darker colour of venous blood in the deeper layers. In 1665 

 it was discovered by Fracassati, a famous physician of Bologna, 

 that the florid colour of the superficial layer of the clot was pro- 

 duced by the action of the air, and that it sufficed to invert the 

 clot for the darker layers, which had been in contact with the 

 walls of the vessel containing it, to assume the same hue as the 

 arterial blood. 



This was confirmed by Lower (1669), another friend and 

 collaborator of Boyle, who at the same time discovered a further 

 weighty fact : he observed, namely, that when artificial respiration 

 was used with the opened thorax, the venous blood became arterial, 

 not in the heart, but in the lungs, while the reduced blood of the 

 lungs also became venous if artificial respiration was interrupted. 



So far nothing positive was known about the chemical processes 

 that take place in respiration, and the analogy between respiration 

 and combustion was merely guessed at, not proven. 



The pioneer in the chemistry of the air and the doctrines of 

 respiration, combustion, and oxidation of metals was John Mayow 

 (1640-1679). In a series of original experiments published at Oxford 

 when he was twenty-eight, he expressed his conviction that the 

 air was not a simple body but a mixture of at least two different 

 gases or " spirits," one of which (termed by him spiritus nitro- 

 aereus or igneo-aereus) is competent to support life by passing into 

 the blood during respiration, and rendering it florid and able to 

 ferment and develop heat. It is this same vital gas which 

 combines with burning bodies, generates acids, and rusts iron. 

 The air that remains after the consumption of the spiritus nitro- 

 aereus is inadequate for life, for combustion, for the rusting of 

 metals. The experiments by which Mayow was led to these 

 remarkable results, which virtually involved the discovery of 

 oxygen and nitrogen, consisted chiefly in the introduction of small 

 animals and lighted candles into a closed vessel over water. He 

 noted the diminution of the volume of air in consequence of 

 respiration and combustion, and the cessation of life and of 

 combustion after a certain time, due not to the accumulation of 

 fumes, but to the consumption of the igneo-aereal particles. 

 Unfortunately this genius, who antedated the greatest discovery 

 of the chemistry of the air by a century, died at the age of thirty- 



