8 RESPIRATION 



only reply, following the example of Hippocrates who protested 

 against the intrusion of abstract philosophical speculatTons 'int&' 

 medicine, that there can be no doubt about the existence. of the 

 associated and persistent group of appearances which the woriL 

 <^vsto- designates when applied to life. If we ignore this we reject 

 the one thing which gives us that grasp of biological phenomena 

 which enables us to predict them, and renders a scientific treatment 

 of biology and medicine possible. 



The immediate subject of this book is the side of physiology 

 which concerns the means by which the supply of oxygen and 

 removal of carbon dioxide are so carried out and regulated that 

 physiological requirements are met. That this supply and removal 

 are through the lungs and blood has already been pointed out; 

 but the development of knowledge as to the means of regulation 

 must now be traced. Much difficulty arises, however, from the 

 fact that the problem itself was only recently realized with any 

 clearness. Respiration and circulation have been to a large extent 

 treated as if the requirements of the body were on the whole 

 constant. Actually, however, the consumption of oxygen _aiid. 

 production of carbon dioxide fluctuate greatly. A heavy exeriioiij 

 for instance, will increase tenfold the consumption of oxygen and 

 output of carbon dioxide for the whole body, and must certain,!)^ 

 increase in a far higher ratio the consumption and output of the 

 muscles actually at work. 



It has of course been known from the earliest times that muscu- 

 lar activity causes great increase in the depth and frequency of 

 the breathing, and that rebreathing the same air has a similar 

 effect ; but the very familiarity of these facts seems to have led 

 to a relative neglect of the problem of how the respiratory activi- 

 ties are regulated. An undue specialism has led to the investiga- 

 tion of each form of bodily activity as if it were something 

 separable from other bodily activities, and not a physiological 

 activity. Further confusion has arisen through the roughness of 

 many of the experiments made on animals, and corresponding 

 failure to detect the delicacy of physiological regulation. 



In i8i I it was discovered by Legallois that if a portion of tissue 

 definitely localized in the medulla oblongata is destroyed respira- 

 tion ceases and death ensues. ^^ This part of the medulla has come 

 ; to be known as the respiratory center^ and round the responses of" 

 this "center" to various nervous and other stimuli the physiologi- 

 cal investigation of breathing has been focused. 



" Legallois, Experiences stir la principe de la vie, Paris, 1812. 



