1909.] The Nerves of the Atrio-ventricular Bundle. 157 



dye will at one time select motor endings in preference to sensory or vaso- 

 motor ; at another time, under the same external conditions, the sensory or the 

 vasomotor are the better, and may be the only ones stained well. This 

 appears to me to be due to the particular chemical state of the nerve ending 

 at the moment the dye reaches it. 



The animals used in the investigation have been the calf, sheep, and pig, 

 and to a less extent the dog. Tissue was also obtained from the human 

 heart. I am not prepared at this time to report on the results of the 

 investigation on human material or in the dog, but so far as these have gone 

 I have no reason to believe that they will not bear out the results reported in 

 this paper on the three first-mentioned animals. 



The examination was confined to the part of the bundle extending from 

 near the coronary sinus through the fibrous septum and down both arms. 

 Though this constitutes but a part of the entire bundle, it forms an important 

 section ; it is a well-defined structure and includes the path across the atrio- 

 ventricular septum. To avoid confusion, it is referred to in this paper as the 

 atrio-ventricular bundle. 



Even a very superficial examination convinces one of the important part 

 taken in its composition by nerve elements. Nerve cells are scattered in 

 profusion along its course, and nerve fibres pass in strands along with its 

 muscular elements or intricately interlace around its cells. There is no part 

 of it, from the coronary sinus to the end of its right or left arm, bereft of 

 groups of ganglion cells or devoid of nerve fibres. The neurologist might 

 well refuse to recognise in it a muscle bundle ; to him it might become 

 conspicuously a nerve pathway of very intricate structure. 



In the bundle the nerve elements divide themselves for descriptive 

 purposes into three groups : 



L Ganglion cells. 

 II. Nerve fibres and plexuses. 



III. Nerves directly associated with the blood-vessels. 



L The ganglion cells are naturally first described, for they are the most 

 conspicuous nerve structures present, both from their abundance and their 

 size. They are found usually in groups of varying number ; some of these 

 in the calf have as many as 16 nerve cells, but more may easily be present. 

 Individual cells, scattered either in the course of the nerve strands or 

 isolated in the fibrous tissue around the bundle, are frequently seen. 



Nerve cells are abundant in the atrio-ventricular bundle of all the animals 

 studied, but I have examined them chiefly in the calf, where, from their large 

 •■^ize and from the facility with which they stain, they are especially suitable 



