5Q THYSIOLOGY OF MUSCLES AND NERVESo 



did not begin at the point z, but at some little distance 

 beyond this, at a. From this it is to be inferred that 

 the contraction of the muscle did not begin at the 

 moment of irritation, for it is evident that the cylinder 

 of the myograph had time to turn from z to a before 

 the indicator was raised by the contraction of the 

 muscle. A certain time, therefore, elapses before the 

 change produced in the muscle by irritation results -in 

 contraction. The duration of this time — which can be 

 accurately calculated from the length of the space exist- 

 ing between z and a — is about one-hundredth of a 



/T a C 



Fig. 18. The curvks of a muscle-pui.satiox. 



second. This stage is called that of latent irritation, 

 for during it the irritation has not yet become actively 

 efficient in the muscle. From the point a the muscle 

 evidently contracts, as is shown by the rising of the 

 pencil from point a to point 6, which is the highest 

 part of the curve described ; from that point onward 

 the muscle again lengthens till it resumes its original 

 length at the point c. The time which elapses between 

 the beginning of the contraction and its maximum 

 is called the stage of increasing energy ; the time from 

 this maximum to that of the full re-extension of the 

 muscle is that of the stage of decreasing energy. The 

 whole duration of the muscular pulsation from the 

 commencement of the contraction at a till complete 

 extension is again reached at c, is from about one-tenth 

 to one-sixth of a second. 



