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CHAPTER V. 



RESPIRATION 



he" ancients speculated upon the physiology of respiration; 

 Aristotle (384 B. C.) contended that the function of breathing was to 

 aol the blood. It was noticed that animals over-heated from exertion 

 breathed more rapidly, hence the inference. Galen (131-203 A. D.) 

 also maintained that the air inspired served to regulate and to cool 

 down the innate heat of the heart; that the peculiar action of the 

 chest wall seen in respiration introduced into the blood the air re- 

 quired for the regeneration of vital spirits in the left side of the 

 heart, whence by the arterial route they were distributed through- 

 out the body. Galen also recognized the necessity of ridding the body 

 of "fulginous vapors'* produced by the innate fire in the heart which 

 act was accomplished by expiration. In the latter part of the fifteenth 

 century, Leonardo da Vinci, painter, mathematician and naturalist, 

 disproved the fallacy that air simply cooled the blood in respiration. 

 He found that air was consumed by fire and that animals could not 

 live in a medium incapable of supporting combustion. This is the 

 first record in the history of science which pointed to the fact that 

 the function of air in respiration depended upon its chemical com-, 

 position and not upon its physical properties. 



r^ It is evident that no real advance could be made in the physiology^ 

 \of breathing until the circulation of the blood had been demonstrated. 

 Furthermore, this department of the science of physiology lagged 

 until the chemist appeared on the scene. Harvey had pointed out 

 that as the blood went to the lungs from the right side of the heart 

 thence to the left auricle a marked change took place, the blood as- 

 suming a bright arterial hue. The cause which resulted in this 

 peculiar change, Harvey was unable to discern, nor did it become 

 known until a much later day, when scientists became familiar with 

 the characteristics and constituents of atmospheric air. 



Mechanics of Respiration. The first real knowledge on 

 the mechanics of respiration we owe to Borelli. Applying 

 the knowledge of muscular contraction on the one hand, 

 and atmospheric pressure on the other, he taught that inspira- 

 tion consisted of the entrance of air into the chest by virtue of at- 

 mospheric pressure, the thorax being enlarged by the muscular con- 

 traction of its walls; expiration consisted mainly in a cessation of 

 muscular contraction. Borelli broke with the ancient view that the 

 function of breathing was the cooling of the excessive heat of the 

 heart or the ventilation of the vital flame. "So great a machinery 

 and vessels and organs of the lungs," he continues, "must have been 

 instituted for some grand purpose ; and that we will try to expound, 

 if possible, though we shall stammer as we go along." Again he in- 

 , sists, "Air taken in by breathing is the chief cause of the life of ani- 

 j mals." It is more important than the heart and the circulation of the 

 blood. 



