SEQUENCE OF CONTRACTION OF PARTS OF HEART. 185 



Such is asserted to be capable of experimental proof, and is the strongest 

 argument used against the sequence being simply due to the passage of a wave 

 of contraction. Two methods have been especially prominently brought 

 forward by Engelmann. 1 



1. Biedermann 2 has shown that ordinary striated muscle can be completely 

 deprived of all power of shortening its fibres, without any loss of its excitability 

 to electrical stimulation, or its power of conduction, by soaking it in ordinary 

 water, so that the part of the muscle so treated behaves to the rest of the 

 muscle like a motor nerve. Engelmann has made trial of this same method in 

 the case of the heart, and asserts that if the auricles and sinus of the isolated 

 heart are dipped under water, while the ventricle is left free and its contractions 

 are registered, then, after a time, the auricles lose all muscular character, and 

 behave as though they were motor nerves to the ventricle ; each stimulus of 

 the auricle producing a contraction of the ventricle without the slightest trace 

 on the ventricular curve of any antecedent auricular contraction. 



2. Engelmann has sometimes succeeded in reducing the contractions of the 

 auricles to invisibility, while the contractions of the ventricle still continue, by 

 means of a reflex stimulation of the vagus nerve on the heart, in consequence of 

 stimulation of the wall of the stomach. This implies, according to him, that 

 the normal impulse from the sinus can reach the ventricular muscle, and cause 

 it to contract without any necessary intermediate contraction of the auricular 

 muscle. 



To my mind it is very doubtful whether either of these experiments are 

 conclusive, for the simple reason that it is very difficult to be quite certain 

 that no contraction passes along any part of the auricle. 



The difficulty of being certain that no part of the heart is contracting, when 

 it is apparently absolutely still, was brought home to me very strongly when I 

 was making the experiments recorded on p. 217, for the purpose of seeing 

 whether the accelerator (augmentor) nerve was able to make a quiescent heart 

 beat again ; as mentioned there, I was deceived again and again ; in each case 

 the heart was apparently absolutely motionless, stimulation of the nerve made 

 it beat vigorously. Any graphic method, such as that used by Engelmann, 

 would most certainly have led to the conclusion that the augmentor nerve 

 was able to set up rhythmic contractions in the non-beating heart, and yet 

 such a conclusion would have been wrong, for in every case examination of the 

 sinus with a powerful lens showed that the heart had not really ceased to beat, 

 but only that the beats, which were perfectly regular, were confined to in- 

 finitesimal movements of the muscular tissue of the sinus. So also with respect 

 to the vagus nerve, I have shown in my paper in the Philosophical Trans- 

 actions (Fig. 1 2, a and b) that the vagus is able upon stimulation to reduce the 

 contractions of the auricle to invisibility, as far as registration on a blackened 

 surface goes, and yet, from the very comparison of 126 with 12a, I feel sure 

 that in both cases the auricle was contracting. 



Again, Mac William 3 has pointed out that a contraction wave may travel 

 from the sinus to the ventricle in the case of such a heart as that of the 

 tortoise or eel in two different Avays (1) Over the auricular tissue proper, i.e. 

 the reticulated portion ; (2) over the flattened basal part of the two auricles or 

 sinus extension. If then, as is possible, the septum between the auricles in 

 the frog's heart corresponds to the sinus extension of the tortoise's heart, a 

 contraction might reach the ventricle through the muscular tissue of the 

 septum, while the auricles proper remained absolutely quiescent. 



Engelmann, too, has demonstrated most conclusively that the rate of travel 

 of the wave of stimulation over the heart is strong evidence that such wave 



1 Arch. f. d. r/cs. PhysioL, Bonn, 1894, Bd. Ivi. S. 199. 



2 Sitzunt/sb. d. k. Akad. d. Wissensch., Wien, 1888, Bd. xcvii. S. 101. 



3 Journ.' PhysioL, Cambridge and London, 1885, vol. vi. p. 192. 



