CHAPTER I 

 Historical Introduction. 



IN the history of physiological discovery the growth of knowledge 

 as to the physiology of breathing was comparatively late. Before 

 the middle of the seventeenth century hardly anything was known 

 about breathing except its muscular mechanism and the facts 

 that if the breathing of a man or higher animal is interrupted 

 for more than a very short time death ensues, and that the breath- 

 ing is increased by exertion and by some diseases. The discovery 

 by Harvey of the circulation threw no positive light on the physi- 

 ology of breathing, and it was still generally believed that the 

 main function of respiration is to cool the blood. Progress was 

 impossible without corresponding progress in chemistry, 



The first beginnings of a better knowledge date from the work 

 at Oxford of Robert Boyle 1 and Mayow 2 a young doctor. Boyle 

 showed with the air pump that air is necessary to life, and Mayow 

 investigated and compared together the influences of niter in the 

 combustion of gunpowder, and of air in respiration and ordinary 

 combustion in air. He drew the conclusion that in all of these 

 processes a "nitro-aerial spirit" combines with "sulphur" (com- 

 bustible matter). As regards respiration he concluded that the 

 nitro-aerial spirit is present in limited proportion in air, and is 

 absorbed from the air in the lungs by the blood, carried by the 

 circulation to the brain, where it is separated off in the ventricles, 

 and thence passes down the supposed nerve- tubules to the muscles, 

 where it unites with "sulphur" and produces muscular contraction 

 by the resulting explosions. He explained the increased breathing 

 which accompanies muscular exertion as a necessary accompani- 

 ment of the increased consumption of the nitro-aerial spirit. 



It will thus be seen that he had practically discovered oxygen r 

 in so far as the rudimentary chemical ideas which he had formed 

 permitted the discovery. He had also formed a sound physiological 

 conception of the relation between muscular work and increased 

 breathing. Mayow's conception of oxygen passing down the 



1 Boyle, New ex-pertinents physico-mechanical, touching the Spring of the Air, 

 Oxford, 1666. Particularly Experiments XL and XLI, with the accompanying 

 "Digression containing some Doubts touching Respiration." 



51 Mayow, Tractatus Quinque Meciico-physici, Oxford, 1673. In particular 

 Tractatus II, De Respiratione (26. Edition). 



