74 PHYSIOLOGY OF MUSCLE AND NERVE 



than 0.5-1.0 second. In accordance with this result, it is generally 

 beUeved that our voluntary contractions bear a close resemblance 

 to the tetanus of excised muscle. This would imply that even our 

 briefest muscular movements are the result of a series of stimuH sent 

 into the muscle at regular intervals during the continuance of its con- 

 traction. From this it may be inferred in turn that even the shortest 

 contractions of our muscles are composed of a number of simple 

 twitches. This inference is strengthened by the observation that a 

 contracting muscle emits a sound which possesses a vibration frequency 

 of 30-40 in a second. This discontinuity of the contractions of our 

 skeletal muscles is indicated further by the curve recorded by our fin- 

 gers when held in voluntary tetanus. When registered upon a slowly 

 revolving drum, this curve invariably exhibits irregular oscillations, 

 such as occur in the course of general spasms of the musculature 

 resulting from irritations of the central ganglion cells. Quite similarly 

 it has been shown by Piper ^ that if a string-galvanometer is applied 

 to the flexor muscles of the forearm, the stimulation of the median 

 nerve elicits a typical diphasic deflection of the needle. It was also 

 found that the voluntary contraction of these muscles gives rise to 

 about 40 or 50 of these diphasic variations in the course of a second. 

 Other muscles gave similar results. By connecting this instrument 

 with the phrenic nerve, Dittler has proved that the diaphragm may 

 be contracted by a discharge of impulses possessing a frequency of 

 50 to 70 in a second. 



These results indicate very clearly that a muscle does not contract 

 in consequence of the influx of a single stimulus, but in consequence of 

 a series of stimuli. It must be evident, therefore, that the motor cells 

 innervating a muscle always discharge a series of impulses which give 

 rise to a serial evolution of muscular energy. Their discontinuance 

 then permits the relaxation to set in. The analogy between a volun- 

 tary contraction and one produced in excised muscle by artificial 

 stimuli, is therefore a very close one. These statements may also be 

 appHed to the tonus of muscle, with this modification, however, that 

 the stimuli upon which the tonic condition of muscle tissue depends, 

 are of subminimal intensity. These rhythmic discharges by the cen- 

 tral ganglion cells give rise to a discontinuous evolution of energy 

 which just suffices to keep the mus.cle in a semi-active condition, ready 

 to respond to any supraminimal stimuli that may impinge upon its 

 neuromuscular junction. 



Contracture. — The term contracture signifies that the relaxation 

 of the previously contracted muscle is unduly prolonged, or, as may 

 also be said, that its contraction is maintained for an abnormally 

 long time. This condition is frequently encountered during fatigue, 

 or when a fresh muscle is cooled or is subjected to excessive stimulation. 

 It may also be produced in a chemical way by the administration of 

 small doses of veratrin or barium, and, in a lesser degree, also by 

 1 Pfluger's Archiv, cxix, 1907, 301, and Archiv fiir Physiol., 1914, 345. 



