TETANUS. 



567 



muscles by more than 30, human muscles by from 8 to 12, the sluggish abductor 

 minimi digiti of man by 6 shocks in a second. The muscles of birds are not 

 thrown into a state of tetanus even by 70 shocks, and the muscles of insects not 

 even by from 350 to 400 in a second. In the muscles of the crab's claw, rhythmic 

 contractions or rhythmically interrupted tetanus (in the astacus and hydrophilus) 

 are observed as a result of tetanic stimulation. 



O. Soltmann found that the white muscles of new-born rabbits are tetanized 

 by 1 6 shocks in a second, and that the tetanus thus induced resembles that of 

 fatigued adult muscles. This fact explains the readiness with which tetanus 

 occurs in the new-born. 



Curarized muscles are at times thrown into a state of tetanic contraction 

 by a momentary stimulus. 



The extent of shortening in a muscle in a state of tetanic contraction is, 

 within certain limits, dependent upon the strength of the individual stimuli, and 

 also upon their frequency. The steepness of the tetanus-curve increases with 

 increase in the strength of the stimuli rather than with increase in the frequency 

 of the individual stimuli. With feeble stimuli the muscle exhibits greater con- 

 tinuity in its contraction; intensification of the stimuli then causes a greater 

 discontinuity in the curve (tendency to clonic spasm) ; and if the intensity of 

 the stimuli be still further increased the curve becomes again more nearly con- 

 tinuous. The contracture that may remain after tetanus is the more marked the 

 stronger and longer the stimulation and the weaker the muscle. The height of 

 the contraction and that of tetanus are the same for an unweighted muscle. Only 

 in the case of the weighted muscle is the height of the single contraction less 



FIG. 196. I, Fluctuations during a continuous contraction of the flexor brevis pollicis and the abductor pollicis. 



II, of the extensor digiti tertii. 



than that of the tetanic contraction. At times a stimulus applied immediately 

 after tetanus has a greater effect than one applied before tetanus. 



The tetanized muscle cannot maintain the same degree of contraction in- 

 definitely if the succession of shocks remains the same. On the contrary, it will 

 lengthen somewhat as fatigue sets in, at first rapidly, but later more slowly. 

 If the tetanizing stimulus is withdrawn, the muscle does not immediately regain 

 its natural length, but a certain contraction-remainder persists for some time, 

 especially after long-continued induction-shocks. 



Muscle may also enter into a state of permanent contraction, which has not 

 been definitely determined to be due to fusion of single contractions ; for example 

 the transient contraction induced by certain chemical agents (such as ammonia 

 and others), the elevations attending idiomuscular contraction, and that induced 

 by the passage of a constant current. 



If rapid, weak induction-shocks (more than 224 and 360, even as many as 

 5000 in a second for frogs' muscles) be applied to the muscle or its motor nerve, 

 the tetanus may cease after the initial contraction. This occurs with the least 

 frequency of stimulation when the nerve is cooled; the higher the temperature 

 of the nerve the greater the frequency of stimulation that may still be effective 

 in inducing a long-continued tetanus. 



This initial contraction is a short tetanus; increase in the strength of the 

 current renders the tetanus continuous. On the other hand, Kronecker and 

 Stirling, however, observed tetanus occur with more than 24,000 shocks in a 

 second. According to these investigators, the upper limit of frequency for the 

 muscle that will still cause tetanus appears to lie near the limit at which fluctua- 

 tions in the current can no longer be appreciated, even with other rheoscopes. 



