36 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



striking way one of the general characteristics of living matter, 

 namely, that every effective stimulus applied to it leaves a record, 

 so to speak. The muscle in this case is in a changed condition 

 .after each stimulus, as is indicated by the difference in its re- 

 sponse to the succeeding stimulus. While it cannot be said that 

 a similar effect has been shown in all tissues, still the evidence in 

 general points that way, and some of the complicated phenomena 

 exhibited by living matter, such as memory, habits, immunity, 

 etc., are referable in the long run to this underlying peculiarity. 



Lee has discovered the interesting fact that while in frog's muscle, as a 

 rule, fatigue is accompanied by a prolongation of the curve, especially of the 

 phase of relaxation, this does not hold for mammalian muscle. In the latter 

 muscle the successive contractions become smaller as fatigue sets in, but their 

 duration is not increased. 



The Contraction Wave. Under ordinary conditions the fibers 

 of a muscle when stimulated contract simultaneously or nearly so, 

 and the whole extent of the muscle is practically in the same phase 

 of contraction at a given instant. It is comparatively easy to 

 show, however, that the process of contraction spreads over the 

 fibers, from the point stimulated, in the form of a wave which moves 

 with a definite velocity. In a long muscle with parallel bundles of 

 fibers one may prove, by proper recording apparatus, that if the 

 muscle is stimulated at one end a point near this end enters into 

 contraction before a point farther off. Knowing the difference in 

 time between the appearance of the contraction at the two points 

 and the distance apart of the latter, we have the data for determin- 

 ing the velocity of its propagation. In frog's muscles this velocity 

 is found to be equal to 3 or 4 meters per second, while in human 

 muscle, at the body temperature, it is estimated at 10 to 13 meters 

 per second. Knowing the time it takes this wave to pass a given 

 point (d) and its velocity (v), its entire length is given by the 

 formula I = vd. In the frog's muscle, therefore, with a velocity of 

 3000 mm. per second, and a duration of, say, 0.1 second, the 

 product (3000X0.1=300 mms.) gives the length of the wave or 

 the length of muscle which is in some phase of contraction at any 

 given instant. Under normal conditions the muscle fibers are 

 stimulated through their motor plates, which are situated toward 

 the middle of the fiber, or perhaps one muscle fiber may have 

 two or more motor plates, giving two or more points of stimula- 

 tion. It follows, therefore, from this anatomical arrangement 

 and the great velocity of the wave that all parts of the fibers 

 are in contraction at the same instant and, indeed, in nearly the 

 same phase of contraction. Under abnormal conditions muscles 

 may exhibit fibrillar contractions; that is, separate fibers or bundles 

 of fibers contract and relax at different times, giving a flickering, 

 trembling movement to the muscle. 



