THE SHEATH OF THE BUNDLE OF HIS 57 



evidence has been shown to prove that the fasciculi of the bundle 

 are separated from the heart muscle by connective tissue. Dogiel 

 also states that the endocardium is not sufficiently transparent 

 so that the fasciculi of the bundle and connective tissue sheath 

 can be seen with the unaided eye! 



The subject of the 'Sinus-knoten/ upon which Keith and Flack, 

 Keith and Mackenzie, Fahr, Monckeberg, Koch, Thorel and 

 Wenkebach have done recent investigations, and the relations of 

 the ' Sinus-knoten' to a connective tissue sheath, are not con- 

 sidered in this article, for the writer has sought to limit himself 

 to the relations of the connective tissue sheath of the 'Knoten' 

 and the parts of the bundle peripheral to this. 



In the present investigation eighty-seven hearts were used; 

 of these thirty-eight were beef hearts,- thirty sheep, fifteen calf, 

 and one was from a lamb six weeks old. About three-fourths of 

 these hearts were used for injections, and many of them were 

 afterwards dissected. Others were used in part for microscopic 

 work. The rest were used for both gross dissection and micro- 

 scopic work. Pieces of tissue including parts of the bundle with 

 some of the cardiac muscle were removed from regions (where 

 the bundle begins its course from the place) of the 'Knoten,' 

 where the bundle passes under the cartilaginous septum and the 

 main branches pass down upon the latter, and also farther down 

 from regions where the branches of the bundle were very small. 

 Serial sections of the complete system were not made, however, 

 for it was thought that an examination of the bundle with its 

 connective tissue envelope in different regions in a number of 

 hearts would be entirely adequate for the purpose of this investi- 

 gation. The tissues were fixed in formalin or Zenker's fluid, 

 dehydrated, embedded in paraffin, and cut 5 to 7^ and 10 micra 

 in thickness. The ordinary haematoxylin and eosin stain was 

 used, although some sections were stained with Van Gieson. In 

 some instances where tissue was removed for miscropic study after 

 injection of the sheath, the celloidin method was used. 



Since a description of the atrio-ventricular bundle as it is seen 

 by gross dissection would be a useless repetition of what has 

 already been well done by others, it is omitted here. The bundle 

 is easily located and easily dissected from its origin to the terminal 



