I 111 fir. \ 01 i HI in IBTBJ a l 



ond, third, or fourth auricular contraction, i rach a eompleto 



partial heart-block has been instituted, tin- clamp ii rem t will 



usually be found thai the heart-block disapp< and the auri 

 ventricular contractions fall back into their usual sequence The im- 

 portance of tliis discovery, apart from its physiological in 

 the fad thai it is exactly duplicated in < 



tracing of the radial artery is compared with »f the jugulai 



iu certain types of heaii disease, it will be found thai tin- auric 

 ing two or three times more quickly than the venti In man] 



thesi - it has I a t*iiiunl on autopsy that definite lesions often 



litic iu nature involve the auriculoventricular bundle, In 

 however, such lesions have no1 been disc mes the bun< 



is v,, severely diseased thai the block is complete, the venti 

 tracting quite independently of the auricle Stokes-Adams Bynd 

 In Buch cases it is assumed thai the 1 » « - ; 1 1 originates in the uninjured p 

 of the bundle below the seat of the block. It should be pointed "ut h< 

 however, thai all cases of slow pulse in the arterii not i rily 



dependenl upon heart-block, but may depend upon a slow l.. 

 auricle itself. This is called bradycardia. 



9 imetimes after complete destruction of the auriculoventricular bun- 

 die the heat continues to he transmitted to the ventricle, and con 

 this transmission has sometimes been observed to he upset by l< not 



affecting the bundle. The explanation of both of th< ceptional 



suits almosl certainly is that the righl lateral connection described 



•_ r '- 1M the main pathway of transmission for t> 



TIm- facility of conduction through the auriculoventricular bundle 



suhjeet to alteration hy the impulses passing to it ah. 



particularly the left vagus. I ! can also be altered bj certain dr 

 especially digitalis ami Btrophanthin. The clear demi ion that it is 



along this bundle that the heat is transmitted is strong evidence i' 

 of tli.- myogenic hypothewa 1T1 concerning tin 



heai-the.it. hut it does not m ly disprove the m 



. for histological investigation lias shown that tin- bun< 

 surrounded by an intimate plexus of nerve fib< 



Spread of the Beat in the Ventricle 



After the impulse lias been transmitted by the bui 

 tricles, it Bpn the many branches into whicl 



the two main divisions of this huinl rate, 



ventricular musculatn 



ruination of these brand • papillarj m 



contrad before -t "t" Ihe mnselo of ti 



