26 SURGICAL SHOCK 



that the output of the ventricles in shock is small, 

 but this is due to deficient filling, not to impaired 

 contractile power. Once again, then, we must face 

 the crucial paradox of shock, a fall in blood-pressure, 

 in spite of normal heart and contracted peripheral 

 arteries. 



THE ACAPNIA THEORY OF YANDELL 

 HENDERSON. 



During the past few years a most important, if 

 not revolutionary, series of papers has been appearing 

 in an American journal of physiology, by Yandell 

 Henderson and other workers in the Yale school, 

 dealing with surgical shock in animals. 



Because carbon dioxide is exhaled from the body 

 by the lungs ; because, in conditions of asphyxia, the 

 amount of the gas is greatly increased in the blood, 

 it has perhaps been too readily assumed that it is 

 nothing but a poison, and serves no useful purpose 

 in the body and in the blood. Haldane and Priestley 

 showed several years ago, that the activity of the 

 respiratory centre depends, in ordinary circum- 

 stances, entirely on the CO.^ content of the blood. 

 When tliis rises above a certain figure, constant for 

 the individual, respiration is stimulated. This is the 

 cause of each succeeding breath we draw. The gas 

 is being furnished to the blood by the muscles, glands, 

 and other tissues continuously ; each movement of 

 expiration reduces the blood content. In violent 

 exercise the breathing is excessive because more C0„ 

 is given off by the tissues ; after a swim under water 

 it is excessive because the gas has been accumulating. 



