CHAP, iv.] 



THE VASCULAR MECHANISM. 



191 



is the diastole diminished but the systole is actually shortened. 

 Our knowledge of these 'accelerator' nerves is however too im- 

 perfect to be dwelt upon here. 



Other modifying agents. The beat of the heart may also be 

 modified by influences bearing directly on the nutrition of the 

 heart. The tissues of the heart, like all other tissues, need an 

 adequate supply of blood of a proper quality; if the blood vary 

 in quality or quantity the beat of the heart is correspondingly 

 affected. The excised frog's heart, as we have seen, continues to 

 beat for some considerable time, though apparently empty of blood. 



FIG. 42. THE LAST CERVICAL AND FIRST THORACIC GANGLIA IN THE DOG. 



The cardiac nerves of the Dog. The fignre is largely diagrammatic, and represents 



the left side. 



f. sym. the united vagus and cervical sympathetic nerves, gl. cerv. i. the 

 inferior cervical ganglion, n. v. the continuation of the trunk of the vagus. 

 ann. V. the two branches forming the annulus of Vieussens round the subclavian 

 artery, art. subcL, and joining gl. th. pr., the first thoracic or stellate ganglion (the 

 branch running in front of the artery is considered by Schmiedeberg to be an especial 

 channel of accelerator fibres), sym thorac. the sympathetic trunk in the thorax 

 r. vert, communicating branches from the cervical nerves running alongside the 

 vertebral artery, the rami vertebrales. n.. rec. the recurrent laryngeal. n. c. cardiac 

 branches from the lower cervical ganglion, accelerator nerves of Schmiedeberg. n'. c'. 

 cardiac branches from the first thoracic ganglion, accelerator nerves of Cyon. n". c". 

 cardiac branch from recurrent nerve, r. rec. branch from lower cervical ganglion to 

 the recurrent nerve, often containing accelerator fibres. 



After a while however the beats diminish and disappear; and their 

 disappearance is greatly hastened by washing out the heart with a 

 normal saline solution, which when allowed to flow through the 

 cavities of the heart readily permeates the tissues on account of 

 the peculiar construction of the ventricular walls. If such a 



