GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 73 



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 

 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 



FIG. 32. 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.) 



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 If the stimulation be withdrawn, the muscle does not at once 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



If the stimulation be still further increased in frequency, the individual 

 contractions become fused together and the curve described by the lever 

 becomes a continuous line. (See Fig. 32.) Notwithstanding the fact 

 that the individual contractions are no longer visible, it can be shown by 



FIG. 33. DEVELOPMENT OF FATIGUE AND CONTRACTION. Muscle stimulated once a second by 



a strong induced current. 



other methods that the muscle is undergoing a series of slight alternate con- 

 tractions and relaxations or vibrations at least. After a varying length of 

 time the muscle becomes fatigued, relexas, and returns to its natural con- 

 dition even though the stimulation be continued. The number of stimuli 

 per second necessary to develop complete tetanus will depend under normal 

 circumstances on the period of duration of the individual contractions. 

 The longer this period, the less the number of stimuli required, and the 

 reverse. Hence the number of stimuli will vary for different classes of animals 



