58 PHYSIOLOGY 



CHAP. 



Schenck justly remarks of Treves' method that, while it corrects 

 certain faults of the original ergograph, it introduces new com- 

 plications. Obviously, as Treves himself admits, contractions 

 against different loads cannot be compared, because with variations 

 of the weight raised the energy of innervation must also vary, 

 other conditions being equal. 



Schenck resumed the study of muscular fatigue (1900) in 

 voluntary effort by applying the isometric method to the abductor 

 of the index finger. For this purpose he used the apparatus 

 devised by Fick in 1887 (Spannungszeichner), with the addition 

 of certain useful modifications. The subject, working by the 

 beats of a metronome, throws this muscle into maximal tension 

 for one second, and relaxes it for the next second. Each series 

 lasts for twenty-five minutes, and therefore consists of 750 alter- 

 nate contractions and relaxations. 



The results of these researches may be summed up as follows : 

 The curve of the isometric contractions of the abductor indicis, 

 made with maximal voluntary effort, generally presents three 

 distinct stages : 



(a) In the first stage the tension which the muscle reaches in 

 the first contractions (which may exceed 14 kgrms.) diminishes 

 rapidly, and drops to about two-thirds (i.e. to 8400 grms.) after 

 about five minutes. 



(b) In a second much longer period (about fourteen minutes) 

 the tension reached by the muscle is approximately constant. 



(c) In a third period the tension drops again, but slightly (to 

 about 7700grms.)tb the end of the series, which may exceed twenty- 

 five minutes, without any further evidence of fatigue in the muscle. 



If these results are compared with those of Treves, it is seen 

 at once that Schenck's first stage corresponds with the descending 

 phase of Treves' ergogram, and the second stage with the constant 

 phase which Treves obtained with the so-called " terminal maximal 

 load," with this difference, that in Schenck's method the maximal 

 energy of innervation is exerted from the beginning to the end, 

 while in Treves' method the energy of innervation gradually 

 declines. Accordingly, there is never any sign of fatigue after 

 the constant phase, and the third stage, which is prominent in 

 the isometric method, does not appear. 



The functional constancy, that is, the comparative non-fatigu- 

 ability and inexhaustibility of muscle, contracting rhythmically 

 both with Treves' ergographic and Schenck's isometric method, 

 recalls the continuous rhythmic activity of the heart and respira- 

 tory muscles. This certainly depends on the blood-supply that 

 restores the muscle and nerve-centres as fast as they become 

 fatigued, and carries off the waste-products. In fact, when excised 

 muscles of the frog are used, the so-called fatigue curve passes 

 into complete exhaustion (Fig. 7, p. 12). 



