[mines] CIRCULATING EXCITATIONS IN HEART MUSCLES 47 



graphy. Fig. 1. is enlarged from one image taken from a cinemato- 

 raph film of an auricle ring exhibiting circulating excitation. 



I have also succeeded in producing excitations in rings of mam- 

 malian ventricle. In many cases I have failed to get the requisite 

 conditions, but in seven experiments on the ventricles of large dogs 

 and in one cat's heart I have been able to demonstrate conclusively 

 the production of true circulating excitations. In the best experi- 

 ments the procedure was as follows: — 



The heart was excised from the anaesthetised animal (usually 

 at the conclusion of some other experiment) and placed on a glass 

 table. The right side of the ventricular wall was then cut out. The 

 act of cutting generally provoked fibrillation. In the sheet of muscle 

 thus obtained a large hole was cut (see Fig. 2.) During this operation 

 the fibrillation died out and the preparation became quiescent. The 

 rest of the experiment followed a course similar to that described 

 above for the auricle rings, except that the time during which the 

 muscle remained excitable was very much shorter. 



In a favourable experiment the vigorous circulating wave and its 

 instantaneous arrest by section of the ring is a sight not easily for- 

 gotten. 



Garrey 1 has recently described experiments made about the same 

 time and independently of mine, on the production of circulating 

 waves in rings cut from the base of the ventricles of large water 

 turtles. 



Garrey has succeeded in getting a number of waves following 

 one another round the ring at the same time — just as Mayer did 

 with the Medusa rings. This very interesting effect evidently de- 

 pends on two factors, the large size of Garrey 's ring, and the fact 

 that when starting the wave the tissue was fibrillating and therefore 

 ready to give the type of wave characteristic of the very active tissue 

 — a short wave slowly propagated. 



Garrey very justly emphasises the fact that for a circulating 

 wave a uni-directional block is a necessary condition. In his experi- 

 ments he was able to demonstrate uni-directional block repeatedly : 

 "it appeared to be related to the irregular width of the blocking 

 and consequently the differences in strengths of the inpulses passing a 

 given point of block." Erlanger had previously noted uni-directional 

 block in strips of auricle. In the frog's heart, when exhausted, I 

 have occasionally observed uni-directional block between auricles and 

 ventricle. In some cases the direction blocked was from ventricle to 

 auricle; in other cases from auricle to ventricle. In the latter case it 

 is very curious to see the auricular contractions not followed by 

 'Amer. Journ. Physiol. 33. March 1914. p. 397. 



