TETANUS OF MUSCLE. 



485 



III. Tetanus Summation of Stimuli. If stimuli, each capable of causing a 

 contraction, and following each other with medium rapidity, be applied to a 

 muscle, the muscle has not sufficient time to elongate or relax in the intervals of 

 stimulation. Therefore, according to the rapidity of the successive stimuli, it 

 remains in a condition of continued vibratory contraction, or in a state of tetanus. 

 Tetanus is, however, not a continuous uniform condition of contraction, but it is a 

 discontinuous condition or form of the muscle, depending upon the summation or 

 accumulation of contractions. If the stimuli are applied with moderate rapidity, 

 the individual contractions appear in the curve (fig. 331, II) ; if they occur rapidly, 

 and thus become superposed and fused, the curve appears continuous and unbrokeu 

 by elevations and depressions (fig. 331, III). As a fatigued muscle contracts 

 slowly, it is evident that such a muscle will become tetanic by a smaller number of 

 stimuli per second than will suffice for a fresh muscle (Marey). All muscular 

 movements of long duration occurring in our bodies are probably tetanic in their 

 nature (Ed. Weber). 



[Summation of Stimuli. If a stimulus, insufficient in itself to cause contraction 

 of a muscle, be repeatedly applied to a muscle in proper tempo and of sufficient 

 strength, at first a slight and then a stronger or maximal contraction may be 

 produced. This process of summation occurs also in nervous tissue ( 360).] 



[Staircase or "Treppe." Bowditch showed that the cardiac contractions exhibited a "stair- 

 case" character, i.e., the height of the second beat is greater than that of the first; and the third 

 than that of the second (p. 84). The same occurs in the case of the muscles of the frog ( Ticgcl, 

 Minot) and in mammals (fiossbach). Bohr showed that the successive ascending apices in a 

 tetanus-curve have really a staircase Minjmal Maximah sub-maximal. Maximal, 



character, and that its exact iorm is 

 that of a hyperbola. Bohr found 

 that (1) this form the muscle not 

 being fatigued is independent of 

 the strength and frequency of the 

 stimuli. (2) The height of the series 

 of contractions in tetanus is inde- 

 pendent of the frequency of the 

 stimuli, increase of frequency merely 

 causing the staircase to reach its 

 maximum more rapidly. (3) The 

 height of the staircase increases 

 within certain limits with the 

 strength of the stimulus 



Fig. 332. 

 Four groups of contractions, interval 

 seconds, and 5 minutes pause 

 (Buckmaster). 



Buckmaster has confirmed this for simple contractions, but as 



of simulation 2 

 between two groups 



2, when the stimuli are minimal or sub-maximal, there is usually no staircase 



I. 



shown in fi v 



character of the contractions, 

 but maximal stimuli always 

 cause it.] 



A continued voluntary 

 contraction in man, consists 

 of a series of single con- 

 tractions rapidly following 

 each other. Every such 

 movement, on being carefully 

 analysed, consists of inter- 

 mittent vibrations, which 

 reach their maximum when 



a person shivers (Ed. Weber). Fig. 333. 



[Baxt found that the I., vibration obtained from the flexor brevis follicis; II., from 

 simplest possible voluntary the extensor digiti tertii. 



contractions, e.g., striking with the index finger, occupies on an average nearly twice 

 as long a time as a similar movement discharged by a single induction shock.] 



The number of single impulses sent to our muscles during a voluntary move- 

 ment is tolerably variable, during a slow contraction = 8 to 12, and during a rapid 



