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HAND-BOOK OF PHYSIOLOGY. 



commences, as indicated by the line c. This interval, termed the "latent 

 period" (Helmholtz), when measured by the number of vibrations of the 

 tuning-fork between the lines s and c, is found to be about -^fa sec. 



The contraction progresses rapidly at first and afterward more slowly to 

 the maximum (the point in the curve through which the line mx is drawn) 

 which takes yf^ sec., and then the muscle elongates again las indicated by 

 the descending curve, at first rapidly, afterward more slowly, till it attains 

 its original length at the point indicated by the line c', occupying T | T sec. 



The muscle curve obtained from the heart resembles that of unstriped 

 muscles in the long duration of the effect of stimulation; the descending 

 curve is very much prolonged. 



The greater part of the latent period is taken up by changes in the 

 muscle itself, the rest being occupied in the propagation of the shock 

 along the nerve (M. Foster). 



Tetanus. If instead of a single induction-shock through the prepa- 

 ration we pass two, one immediately after the other, when the point of 



FIG. 284. Curve of tetanus, obtained from the gastrocnemius of a frog, where the shocks were 

 sent in from an induction coil, about sixteen times a second, by the interruption of the primary cur- 

 rent by means of a vibrating spring, which dipped into a cnp of mercury, and broke the primary 

 current at each vibration. 



stimulation of the second one corresponds to the maximum of the first, 

 a second curve (Fig. 283) will occur which will commence at the highest 

 point of the first and will rise as high, so that the sum of the height of 



FIG. 285. Curve of tetanus, from a series of very rapid shocks from a magnetic interrupter. 



the two exactly equals twice the height of the first. If a third and a fourth 

 shock be passed, a similar effect will ensue, and curves one above the other 



