70 ELECTRO-PHYSIOLOGY CHAP. 



increase quickly at first, and then more and more slowly (prob- 

 ably in the form of a hyperbola), until they finally reach an 

 asymptotic maximum" (I.e. p. 16), a proposition which Hermann 

 had also put forward (4, p. 108). Cardiac muscle seems, as was 

 said above, at first sight to differ from all the striated, skeletal 

 muscles in its lack of correspondence between strength of excita- 

 tion and magnitude of resulting contraction. It appears from 

 Bowditch and Kronecker (22) that, under all conditions, induction 

 currents of a given intensity produce maximal twitches of the 

 previously resting muscles of the ventricle ; weak stimuli produce 

 no effect, while stronger stimuli elicit no more than the minimal 

 effective stimulus ; minimal stimuli arc therefore, as Kronecker says, 

 at the same time maximal, and even the most careful gradation 

 of the stimulus fails in the heart to produce an incomplete contrac- 

 tion. There seems to be only one exception to this rule, under very 

 special circumstances. Mays (23), e.g., finds that occasionally in 

 the apex of the frog's heart, with higher as well as with lower 

 working capacity, the height of the pulse (twitch) will vary con- 

 siderably with the strength of induction shocks sent in at a 

 uniform rhythm. He obtains this result most certainly when 

 the ventricle is filled with stale blood, and working in the oil-bath 

 of the manometer. 



For the rest we can but agree with Fick when he sees in 

 these peculiarities of cardiac muscle " the extreme development 

 of a property common to every other muscle-fibre," since here 

 also " the breadth of interval in the scale of excitation for sub- 

 maximal twitches stands in no relation to the unlimited portion 

 of the same scale corresponding with the maximal contractions." 

 This in no degree solves the problem of the latter, since it is 

 difficult to see why, beyond a certain limit, any given strength of 

 stimulus should only produce quantitatively equal responses, which 

 never correspond with the outside maximum of contraction. 



Apart from other facts to be discussed later, this is evident ex- 

 perimentally, since what is not produced by increment of excita- 

 tion can be obtained by rhythmical repetition of uniform stimuli. 

 The height of contraction, i.e., may increase under given condi- 

 tions, when uniform induction currents are sent into the muscle 

 at uniform intervals. This striking effect was first observed by 

 Bowditchj again in cardiac muscle, and confirmed by Tiegel and 

 Minot in the skeletal muscle of the frog, liossbach in warm- 



