SURGICAL SHOCK 29 



by which carbon dioxide can be restored, and shock 

 prevented or removed, are ; the infusion into a vein 

 of saHne saturated with CO.^, and the increase of the 

 dead space of the respiratory apparatus by making 

 the animal breathe through a long glass tube, so 

 that there is a good deal of to-and-fro breathing of 

 expired air. 



How then are the fall of blood-pressure and the 

 quickening of the heart to be explained ? 



Crile and Henderson agree that there is no primary 

 cardiac failure. After intravenous transfusion, for 

 instance, the heart is perfectly capable of recovery. 

 Henderson finds the primary cause of the failure in 

 the venous pressure. When there is a reduction of 

 CO2 in the blood, the walls of the veins and the 

 tissues supporting them relax, the pressure in the 

 veins falls, blood accumulates in them, and only a 

 small amount is transmitted to the heart. For a 

 time, by constricting the arteries, a fair blood-pressure 

 can be maintained ; at last the supplies reaching the 

 right auricle become so reduced that the arterial 

 pressure falls, the heart-beat becomes quick, the 

 output is small, and severe shock is now established. 

 The quickened heart-rate may be due to some extent 

 to escape from vagus control, the activity of the 

 vagus centre suffering reduction, like that of the 

 respiratory centre, on account of the low blood- 

 content of carbon dioxide. 



Some other factors of importance require mention. 

 It is well known that operations involving exposure 

 of the intestines, especially if they are handled and 

 pulled about, are apt to induce shock. Henderson 



