ii CHANGE OF FORM IX MUSCLE DURING ACTIVITY 79 



Vertebrates is by no means confined to them, but occurs even more 

 demon strably in smooth, as well as in cardiac, muscle. We have 

 already referred to Fick's experiment of the effect of increased 

 tension from increased loading on the magnitude of contraction in 

 the adductor muscle of Anodonta. The consequences of augmented 

 tension on cardiac muscle are very striking, both in vertebrates and 

 invertebrates. The effects observed are indeed somewhat ambigu- 

 ous, owing to the intracardiac nerves, which, as a rule, govern the 

 normal rhythmical movements of the heart, and whose interference 

 is not easily excluded. The simplest experiments are those with 

 the a-ganglionic ventricle of the frog's heart, which has been 

 separated from the auricle the so-called apex, or with the snail's 

 heart (Helix pomatia), where no ganglion-cells have positively been 

 discovered. Since the apex of the heart like all excised skeletal 

 muscle contracts only on artificial stimulation, otherwise remain- 

 ing permanently quiescent, "it is admirably adapted to experiments 

 on the effect of increased tension of the muscle- wall, from increase 

 of intracardiac pressure on excitability and work yielded. These 

 experiments were first introduced by Ludwig and Luchsinger (34). 

 In order to isolate the pressure effect as far as possible, the apex 

 of the heart was filled with physiological salt solution, liegular 

 rhythmical pulsations of a ventricle, which had previously been 

 quiescent, will usually begin at a pressure of 2050 cm. of water. 

 A small mechanical stimulus is usually required to bring about the 

 first contraction, which is then followed spontaneously by an entire 

 series. The pulsation varies regularly with change of pressure, 

 and is indeed higher within a certain range, in proportion with 

 the pressure (cf. tables of Luchsinger, I.e. 293). Engelmann 

 (35) made similar observations on the equally a-ganglionic bulbus 

 aortse of the frog. The effect of tension of the wall is, however, 

 seen most effectively in the thin- walled snail's heart (36). Even 

 in the living animal, it may be seen that evacuation of the quiescent 

 heart, by snipping it, produces a more or less prolonged pause 

 in diastole, or a much retarded action. If the heart is excised it 

 is evident that every expansion of the relaxed and empty ventricle, 

 however slight, is sufficient either to set up (rhythmical) contrac- 

 tion or to accelerate the beat considerably, so that the force of 

 the individual contractions also must be essentially augmented. 

 The same fact has also been established by Schoenlein (37) for the 

 heart of Aplysia. When the extension is not too weak, and in 



