28 SURGICAL SHOCK 



undeniable, and his blood-gas analyses bear it out in 

 animals. Therefore, when the stimulus ceases, 

 breathing becomes very shallow and occasional, and 

 at the same time the blood-pressure falls and the 

 heart beats quickly. This condition may lead to 

 death, and indeed this is the usual consequence in 

 animals. Henderson's theoretical conclusion as to 

 the cause of death is that it is due to lack of oxygen, 

 the store becoming exhausted before the CO. rises 

 high enough to stimulate the centre into activity 

 again ; but this conflicts with the observation of 

 Haldane and his coadjutors, that when the oxygen 

 tension falls below 13 per cent of an atmosphere, 

 lack of oxygen assumes the power of driving the 

 respiratory centre whatever the CO.^ may be. 

 Perhaps this effect is due to acid products thrown 

 out by the oxygen-starved tissues. 



Apart from the dubious explanation, however, the 

 facts merit careful attention. It is possible in 

 animals, merely by excessive artificial respiration, to 

 reduce the CO. so much that respiration is shallow, 

 the heart becomes rapid, blood-pressure falls, and 

 death ensues in about three hours. On the other 

 hand, when the pulmonary ventilation is reduced, 

 and the carbon dioxide in the blood kept at or near 

 its normal figure, very prolonged operations on dogs, 

 extending over seven hours with the thorax opened, 

 result in little or no shock. The rate of heart-beat 

 and the blood-pressure can be varied exactly with 

 the pulmonary ventilation. It is possible to make 

 analyses of the blood-gases with about 3 c.c. of blood 

 by Barcroft's method, from time to time. The means 



