386 THE PROPERTIES OF STRIPED MUSCLE. 



muscle to a succession of instantaneous stimuli of unvarying strength 

 and frequency, was made by Volkmann, 1 but it was not until ten years 

 later that the elaborate research of Kronecker in Ludwig's laboratory 

 afforded the basis for the more exact knowledge of the subject which we 

 now possess. 2 



The muscle used was the triceps femoris of the frog. It remained 

 in situ, so that the circulation could be maintained, and worked under 

 isotonic conditions, either loaded or after-loaded. The load varied in 

 different series of experiments, but never exceeded 50 grms. The nerve 

 was excited by opening induction currents, of which the direction was 

 reversed between each excitation and the succeeding one, regularity 

 being insured by the employment of automatic arrangements throughout. 

 When the method of after-loading was used, it was established that, 

 under the conditions above described (equal stimuli of equal frequency), 

 the successive diminutions of the excitatory shortening of the muscle 

 were exactly equal ; so that, when the contractions were recorded on a 

 slowly moving surface, the tops of the vertical marks which represented 

 the successive twitches were in a straight line (p. 204). The inclination 

 or slope of this line depends on the frequency of the excitations, so that 

 if at any time during the decline an interval of longer duration occurs, 

 the difference in height between the record of the preceding and of the 

 succeeding twitch is correspondingly diminished. The graphic record 

 therefore shows that in after-loaded muscles the decline is equable 

 throughout, the height to which the weight is raised being diminished 

 by equal amounts, until the muscle no longer shortens to a length less 

 than its equilibrium length / ; for although it continues to contract after 

 this point has been reached, the weight is not lifted, and consequently 

 the contractions are not recorded. In the graphic records of loaded 

 muscle with the weight unsupported, the contractions are recorded 

 until they cease. In this case it is observed that towards the close 

 of the observation the curve of decline becomes more and more concave 

 upwards, approaching the base line (the line which corresponds to the 

 length of the muscle when unexcited, but extended by the weight) 

 asymptotically. It is further found that the load may be varied in 

 different experiments, up to a certain limit, without changing the rate of 

 fatigue, i.e., that the height to which at any moment during the decline 

 the muscle can lift a given load, depends not on the weight which it has 

 up to that moment lifted, and consequently not on the work it has done, 

 but exclusively on the number of times that it has been maximally 

 excited. This result was subsequently confirmed by Kronecker and 

 Gotch 3 as regards exhaustion by tetanus. 



Kronecker found that the triceps would go on contracting more than 

 two thousand times when excited every two minutes. When he diminished 

 the interval to a quarter of a minute, the height of the contractions declined 

 more rapidly. This appeared to be also the case when, with a frequency 

 of six per second, the contractions became eventually blended ; whence 

 it appears that there is no essential difference between the exhaustion 

 produced by tetanus (as seen in the decline of the tetanus curve) and 

 that which results from less frequently repeated stimulations. 



1 Arch. f. Aiiat., Physiol. u. wissensch. Med., Leipzig, 1860. 



2 "Ueber die Erimidung und Erholung der quergestreiften Muskeln," Arb. a. d. 

 physiol. Anst. zu Leipzig, 1871, S. 177. 



' 3 Arch. /. Physiol., Leipzig, 1880, S. 438, 



