THE CIKCULATION OF THE BLOOD 53f> 



The contraction wave will pass over the entire 

 zigzag strip. Normally the wave starts at the 

 base and proceeds to the apex, but by artificial 

 stimulation it can be made to pass from the 

 apex towards the base. A similar result can be 

 secured with the auricle. 



The Transmission of the Cardiac Excitation from 

 Auricle to Ventricle ; Gaskell's Block. The con- 

 traction wave can be seen to begin normally in 

 the sinus and thence to pass rapidly over the 

 auricle ; on reaching the auriculo-ventricular 

 junction there is a distinct pause termed the 

 auriculo-ventricular interval ; finally, the excita- 

 tion reaches the ventricle, and the contraction 

 wave is seen to traverse the ventricular muscle 

 as noted above. The auriculo-ventricular inter- 

 val may be lengthened by any natural or arti- 

 ficial hindrance to the passage of the excitation 

 wave. 



1. Place the Gaskell clamp about the auriculo- 

 ventricular junction. Very cautiously turn the 

 screw until the rubber edge makes a gentle 

 pressure on the cardiac tissues at that point. 



With careful work a degree of pressure will be 

 reached that diminishes the conductivity of the 

 muscle fibres joining the auricle and ventricle so 

 far as to- permit only every second or every third 

 excitation to pass. The auricle will beat with- 



