THE NERVOUS REGULATION OF THE HEART 



977 



influence on the heart, so that after extirpation of the stellate ganglion on 

 each side, the pulse frequently becomes permanently slowed. 



THE ACTION OF ADRENALIN ON THE HEART 

 The medullary part of the suprarenal glands forms and secretes into the 

 blood-stream a substance, adrenaline, which has a marked action both on the 

 heart and blood-vessels and plays therefore an important part in the regula- 

 tion of the circulation. Whether this secretion is a constant one has not yet 

 been fully ascertained, but there is no question that under certain specified 



FIG. 451. 

 In tra ventricular pressure tracings (left ventricle) from dog's heart (heart -lung 



preparation). The scale shows pressure in mm. Hg. 

 a. Under influence of adrenaline. 

 6. Under simultaneous influence of adrenaline and C0 2 (15 per cent.) (PATTERSON^. 



conditions there may be a marked influx of this substance into the blood- 

 stream. The action of adrenaline on any part of the body is practically 

 identical with that of excitation of the sympathetic nerve supply to the same 

 part. Its isolated action on the heart is best studied on the perfused heart or 

 in the heart-lung preparation. On adding T ^ mgm. of this substance to the 

 500 c.c. of blood circulating through the heart-lung preparation, a maximum 

 effect is at once produced and this lasts for 15 to 20 minutes. The action is, 

 like that of the sympathetic nerve, accelerator and augmentor. Through 

 its influence on the sinus or the sino- auricular node the rhythm of the heart 

 is markedly increased, in the dog to about 240 per minute. At the same time 

 the energy of each contraction is increased. This is especially shown in a 

 heart which is beginning to fail and is therefore undergoing a certain degree 

 of dilatation. Directly the adrenaline reaches the heart the contractions 

 become extremely energetic so that the heart rapidly diminishes in volume, 

 the venous pressure falls, and the blood flowing into it at each diastole is 

 thrown out with violence into the aorta. The more powerful beat enables 

 the output of the heart at each beat to be maintained or even increased in 

 spite of the shorter duration of the systole. With each beat the maximum 



