178 THE CIRCULATION OF THE BLOOD 



ascending staircase with gradually diminishing steps will be produced. If 

 we repeat this observation with cardiac muscle, we shall find that the stair- 

 case phenomenon or treppe, as it is called, is very pronounced ; and more- 

 over, in obedience to the all or nothing principle, the treppe is obtained in 

 cardiac muscle whatever may be the relative strengths of the stimuli 

 applied to the heart, provided always that all of them are effective; 

 whereas in the case of skeletal muscle it can be demonstrated only pro- 

 vided the stimuli are of equal strength (Fig. 45). 



3. If an effective stimulus is applied to a skeletal muscle while in process 

 of contraction, as in response to a preceding stimulus, the second stimulus 

 prolongs the contraction produced by the first one. If, however, the second 



Skeletal muscle 



Cardiac muscle 



Fig 45. The effects of successive stimuli on skeletal and cardiac muscle to show the prominence 

 of the staircase phenomenon, or treppe, in the latter. (From T. G. Brodie.) 



stimulus is applied during the latent period* of the first one, it will have no 

 effect that is, the muscle during this period is refractory.! From these 

 results it follows that stimuli succeeding each other during the contraction 

 period will, in the case of skeletal muscle, cause a continuous contraction, or 

 tetanus, as it is called, because the contraction produced by each stimu- 

 lus will add itself to that of its predecessor before any trace of relax- 

 ation has set in. If, however, the second stimulus is applied so late in 

 the contraction period of the first that time is not available for the latent 



*By "latent period" is meant the period after the moment of application of a stimulus during 

 which no effect of that stimulus is observed. 



fBy "refractory period" is meant the time following the application of a stimulus during which a 

 second stimulus develops less than its full effect or no effect at all. 



