THE NUTRITION OF THE HEART 



169 



pressure or tension of carbon dioxide has been found to lie between 5 

 and 10 per cent of an atmosphere. 



That the effect of carbon dioxide in encouraging the relaxation of the 

 heart between beats is dependent upon the change in hydrogen-ion con- 

 centration of the perfusion fluid has been shown by securing the same 

 results in experiments with perfusion fluids to Avhich different quanti- 

 tities of weak nonvolatile acids have been added. These observations are 



Fig. 40. Volume curve of ventricles of cat (lower curve) in a heart-lung perfusion prepara- 

 tion. The air used to ventilate the lungs was replaced between the arrows by a mixture con- 

 taining 20% CO 2 and 25% O 2 . This caused dilatation of the ventricles along with feebler beats 

 and a tendency for the arterial pressure to fall (upper curve). The after effect was an im- 

 provement of the beat. (From Starling.) 



of practical importance because of the light which they throw on the 

 cause of cardiac failure following upon conditions in which there has 

 been excessive removal of carbon dioxide from the blood, as in forced 

 ventilation of the lungs. Yandell Henderson has suggested that sur- 

 gical shock may be, partly at least, due to cardiac failure following the 

 " washing out" of carbon dioxide from the blood by the dyspnea so 

 often incident to the administration of anesthetics in surgical operations. 



