70 TEXT-BOOK OF PHYSIOLOGY. 



the term incomplete tetanus or clonus is applied. A graphic record of an 

 incomplete tetanus is given in Fig. 33. 



In such a tracing it is observed that the second stimulation, occurring 

 before the muscle had time to relax, gave rise to a second contraction, 

 which was superposed on the first; the same result followed the third stimu- 

 lus, the fourth, the fifth, and so on. Owing largely to this summation 

 of the contractions there is a gradual rise in the height of the contraction 

 curve. This condition of the muscle, viz., continued contraction, com- 



FIG. 33. CURVES SHOWING THE ANALYSIS OF TETANUS OF A FROG'S MUSCLE (GASTROC- 

 NEMIUS). The numbers under the curves indicate the number of shocks per second applied to 

 the muscle. There is almost complete tetanus with twenty-five per second, and it is a little lower 

 than the previous one because the muscle was slightly fatigued. (Stirling.) 



bined with diminished power of relaxation, is termed contracture. The 

 tracing also shows that as the stimulus continues, the base line, that con- 

 necting the lowest points of the contractions, gradually rises and takes the form 

 of a curve which increases in height as the stimulus continues. The apex 

 line, that connecting the highest points of the contractions, also rises at the 

 same time, indicating a continuous increase in the height of the contractions. 

 The length of time a muscle will exhibit incomplete tetanus depends on a 

 variety of circumstances, e.g., character of muscle, rate and strength of 



FIG. 34. DEVELOPMENT OF FATIGUE AND CONTRACTION. Muscle stimulated once a second by 



a strong induced current. 



stimulation, etc., but mainly on the rapidity with which the muscle becomes 

 fatigued. With the oncoming of fatigue the muscle begins to relax, and 

 ultimately returns to its normal condition, notwithstanding the continued 

 stimulation. If the stimulation be withdrawn, the muscle does not at once 

 return to its original length but remains more or less contracted for a variable 

 time. This contraction after stimulation is known as the contraction- 

 remainder. 



