566 TETANUS. 



form of movement, resulting from accumulated contractions. If the 

 stimuli succeed one another with only moderate rapidity, the separate 

 shocks may still be recorded in the curve (//). If, however, the stimuli 

 are applied in more rapid succession, the curve has an uninterrupted ap- 

 pearance (///). As a single contraction takes place more slowly during 

 fatigue, it is obvious that a fatigued muscle will be more readily thrown 

 into tetanus by a smaller number of single stimuli than a fresh muscle. 



All movements of considerable duration excited in the human body are thus 

 to be regarded as tetanic, for they are constituted of a series of single contractions 

 in rapid succession. Accordingly, every movement, however steady, will on close 

 observation be found to exhibit intermittent vibration, which reaches its climax 

 in tremor and becomes so conspicuous in cases of paralysis agitans. 



The number of single impulses sent to the muscles of the body in the execution 

 of voluntary movements varies considerably when the contractions are slow 

 from 8 to 14 in a second, when the contractions are rapid from 1 8 to 20, the average 

 being 12.5 in a second. Fig. 196, I, represents a myogram of the left flexor brevis 

 pollicis and the abductor pollicis during a continuous contraction of moderate 

 intensity, recorded on the vibrating plate of a tuning-fork. The wave-like eleva- 

 tions indicate the separate impulses, each dentation being equal to 0.01613 second. 

 II represents a similarly recorded curve made by the extensor digiti tertii. 



n 



FlG. 195. /, Two successive submaximal contractions. 77, A series of contractions induced by 12 induction- 

 shocks in a second. 777 Marked tetanus induced by rapid shocks. 



By the summation of single stimuli, the muscle voluntarily excited slowly to 

 contraction is gradually brought to the desired degree of shortening. It is cus- 

 tomary to effect an exact adjustment of the extent of movement by the develop- 

 ment of resistances through antagonistic muscles, as observations on lean, mus- 

 cular persons show. 



The tetanic contraction that occurs under normal conditions in the intact 

 body has also been shown to be composed of single, successive contractions, as 

 secondary tetanus may result from it; the latter may be induced also from a 

 muscle in a state of strychnin-tetanus. 



If a muscle be connected with a telephone whose wires are attached to two 

 pins, one of which is inserted into the tendon and the other into the tissue of 

 the muscle, a sound will be heard when the muscle is thrown into tetanus, indi- 

 cating that periodic motor processes, that is, successive contractions, are taking 

 place in the muscle. The sound is most distinct when the tetanizing Neef's 

 hammer vibrates about fifty times a second. 



The rapidity with which the successive stimuli must follow one another in 

 order to induce tetanic contraction varies for the different muscles of the body, 

 as well as for those of different animals. 



In the case of the muscles of the frog 15 successive shocks in a second are 

 required on an average to induce tetanus (in the hyoglossus muscle only 10, 

 in the gastrocnemius 27 shocks). If the shocks are feeble, more than 20 in a 

 second are required. The muscles of the tortoise are thrown into a state of tetanus 

 by only 2 or 3 shocks in a second; the red muscles of the rabbit by 10, the white 



