542 PHYSIOLOGY OF THE DOMESTIC ANIMALS. 



versely with the blades of a pair of forceps in the line of incision of 

 the former experiment, the apex will cease to pulsate, though still 

 supplied with its normal excitant and nutriment ; it has been separated 

 from its motor ganglion. If the apex be irritated it will beat, to again 

 become motionless on removal of the irritation. This condition of 

 affairs will remain for an indefinite length of time, even for as much as 

 three weeks the apex of the ventricle motionless and gorged with 

 blood and the rest of the heart contracting normally. If, however, the 

 intra-cardiac pressure be increased by clamping the aorta, the apex will 

 commence to beat, but independently of the rest of the heart and at a 

 slower rate. This being so, if we can be positive that there are no 

 ganglia present in the apex, it must be concluded that the heart-muscle 

 may contract independently of any nervous mechanism. It must not 

 be forgotten, however, that it has not been definitely proved that there 

 are no ganglia in the apex, only they have never been found. The posi- 

 tion then is this : 



A fragment of cardiac muscle containing a motor ganglion will 

 pulsate when removed from the body, and without any artificial stimulus. 

 A fragment of muscular fibre unconnected with a motor ganglion will 

 remain quiescent until it receives some external stimulus. By cutting a 

 heart in halves it will be seen that one part pulsates while the other does 

 not. If this subdivision be carried still further, gradually cutting the 

 heart into fragments until they become microscopic in size, and some of 

 them be placed under the microscope, it will be seen that some fragments 

 are rhythmically contracting and others are motionless ; if the sub- 

 division be carried still further, until the ultimate fibres of the heart are 

 isolated, in nearly all the contracting fibres will be found ganglionic 

 nerve-cells, while none are to be found in those which are motionless. 



The action of the inhibitory ganglion may be seen by exposing the 

 heart of a frog in the usual way, and distending the oesophagus with a 

 short glass rod in order to bring the parts exposed into more prominent 

 view. 



The apex of the ventricle should be seized with a pair of forceps 

 and drawn forward and to the right, after dividing the little connecting 

 band between the posterior surface of the ventricle and the pericardium. 

 With the aid of a delicate aneurism needle, a silk ligature is to be passed 

 between the vena cava inferior and the ventricle and between the vena 

 cava superior and the right auricle in such a position that when tight- 

 ened it will grasp the line of junction, which is marked by a slight 

 groove, of the sinus venosus and right auricle. After seeing that the 

 heart is pulsating rhythmically, the ligature should be suddenly tightened, 

 and it will be found that after a few beats the heart will stop in diastole, 

 while the sinus will continue to pulsate as before. After a few moments 



