ix CAEDIAC MUSCLE AND NEEVES 317 



activity is slower and weaker. Gaskell observed (as above) that 

 with localised warming of the sino- auricular and ventricular 

 segments, acceleration of cardiac rhythm resulted in the first case 

 only. He therefore concluded that when the heart is functioning 

 as a whole, the rhythm proper to the less automatic segments 

 remains latent under normal conditions, and that the more 

 frequent and powerful rhythm of the more automatic segments 

 governs the movements of the entire heart. This is the reason 

 why under normal conditions the contraction wave always travels 

 in the peristaltic direction from sinus to auricles, from auricles to 

 ventricle, from ventricle to bulbus arteriosus. 



With this view we must again contrast the latest results of 

 microscopic work, both on the frog's heart (Bethe), and on the 

 muscular bundle of His in the mammalian heart, where there is 

 found to be an exceptional abundance of nerve elements (Hofniann). 



H. E. Hering has recently (1907) modified his previous 

 opinions, calling attention to other experimental data, which he 

 thinks are better explained on the neurogenic theory. These are 

 as follows : 



(a) In the adult mammalian heart there is a segment which, 

 when isolated from the rest, is incapable of reacting automatically. 

 This is the auricular appendage of the right auricle. It now 

 appears from microscopic researches that this particular part has 

 no ganglionic nerve elements. 



Under certain conditions it can be demonstrated that the 

 automaticity of the mammalian heart, and its capacity for 

 reacting to artificial stimuli, are properties independent of one 

 another. It is possible for a heart in diastolic or systolic arrest to 

 be more excitable to artificial external, than to automatic internal 

 stimuli, and vice versa. 



(c) A small incision in the region of the orifice of the venae 

 cavae, or a single induction shock of minimum intensity in the 

 right auricle, may suspend the automatism of the auricular region 

 of the heart for a considerable period. 



(d) Lastly, Hering has recently discovered that a mammalian 

 heart arrested from any cause whatsoever, is capable of recom- 

 mencing its beats in consequence of the stimulation of the 

 accelerator nerve. He holds that these facts are better explained 

 on the theory of a nervous, than on that of a muscular auto- 

 maticity in the adult mammalian heart. 



VII. It can be demonstrated independently of the neurogenic 

 or niyogenic theory of rhythm that cardiac muscle differs from 

 ordinary skeletal muscle in its peculiar physiological characteristics. 

 Bowditch (1870) was the first to study in Lud wig's laboratory the 

 phenomena exhibited by the apex of the heart (attached to a 

 simple cannula filled with serum, and connected with a recording 

 manometer), when excited by various agencies. 



