IT CHANGE OF FORM IN MUSCLE DURING ACTIVITY 73 



existence. Helmholtz observed that in working with induction 

 currents strong enough to produce the maximum of contraction, 

 the intensity of current may be altered arbitrarily without in 

 any way affecting the time -relations. Tigerstedt finds the 

 latent period of contraction, with direct maximal stimulation 

 from break induction shocks, to be independent of the strength 

 of excitation in non-curarised as in curarised muscle. But 

 within that range of current intensity, in which the height of 

 contraction does increase with the increment of stimulation, the 

 latent period, according to the same author, steadily increases 

 with decreasing height of contraction, at first more slowly, sub- 

 sequently in increasing proportions. This is true of normal, as 

 well as of curarised, muscle. 



The Latent Period of the Entire Muscle and of the Muscle 

 .Elements 



At this point we must attack the question often raised in 

 recent discussions, whether the latency period of the muscle element 

 (i.e. smallest section of a primitive fibre) differs or no from that 

 of the entire muscle (consisting of many fibres). All the observa- 

 tions, after Helmholtz, on the time-relations of contraction, refer to 

 individual muscles in the coarse anatomical sense. But if we 

 look more closely into the mechanical alteration in state of the 

 muscle elements (i.e. least possible segments of a fibre) it is 

 evident that not only the active changes in form and constitution, 

 produced by the excitatory processes, but also the passive dis- 

 position, which results from the interconnection of the individual 

 elements in the continuity of the fibre, must be taken into con- 

 sideration. To a final theory of the muscular process the former 

 only is of immediate importance, but the other factors cannot 

 be neglected, since, as is easy to see, they are essentially 

 significant in the mode of manifestation of the contraction of the 

 entire muscle. It is not difficult to show that on exciting one 

 end of a loaded muscle with parallel fibres, the part farthest 

 from the point of excitation will submit to a considerable 

 extension before it goes into contraction. This is best seen 

 in polymerous muscles (29). If, e.g., the rectus int. maj. of 

 the frog, which has an oblique tendinous intersection towards 

 the centre, is made to hang vertically with the tibial end upper- 



