THE NUTRITION OF THE HEART 



167 



is placed in the carotid artery, and connected to a mercury val^e, 

 whereby the blood-pressure can be regulated by raising or sinking a 

 tube in mercury, and in which the blood is also kept warm until it 

 is returned to the animal by the jugular vein. The circulation is 

 confined to the heart and lungs, and the effect of various conditions 

 on the output studied. Fig. 69 shows a tracing obtained by this 

 means. 



Experiments on the output of the heart show 



1. That within certain limits the systolic output is independent 

 of the resistance. 



2. That under favourable conditions a rise of resistance may in- 

 crease the systolic output. 



FT-* 



,,,.- -- t. ....> v ..r: .. --,, 



FIG. 69. TRACING SHOWING VOLUME OF OUTPUT OF HEART. (Knowlton and Starling.) 



A , Volume of ventricle ; B, arterial pressure ; C, output of left ventricle measured ; 



D, time in seconds. 



3. That with increasing peripheral resistance the systolic output 

 as a rule decreases. 



4. That as the arterial pressure generally increases in spite of the 

 diminished systolic output, the diminution in output per second must 

 be proportionately smaller than the increase in resistance. 



The diminution of the output per second is usually shown most 

 strikingly during the rise of arterial pressure which is occasioned by 

 asphyxia. In the asphyxial condition the heart muscle rapidly fails, 

 and passes into paralytic dilatation; while the output from the ven- 

 tricles is opposed, the venous input is increased by the action of the 

 respiratory spasms. 



In the first stage of asphyxia a large vascular area of arterioles, 



