SEC. 2. THE CHANGES IN A MUSCLE DURING 

 MUSCULAR CONTRACTION. 



The Change in Form. 



We have seen that at the close of the latent period the muscle 

 shortens, that is, each fibre shortens, at first slowly, then more 

 rapidly, and lastly more slowly again. The shortening (which in 

 severe tetanus may amount to three-fifths of the length of the 

 muscle) is accompanied by an almost exactly corresponding thicken- 

 ing, so that there is hardly any actual change in bulk. If a muscle 

 be placed horizontally, and a lever laid upon it, the thickening of 

 the muscle will raise up the lever, and cause it to describe on a 

 recording surface a curve exactly like that described by a lever 

 attached to the end of the muscle. There appears to be a minute 

 diminution of bulk not amounting to more than one thousandth. 



If a long muscle of parallel fibres, poisoned with urari, so as to 

 eliminate the action of its nerves, be stimulated at one end, the 

 contraction may be seen, almost with the naked eye, to start from 

 the end stimulated, and to travel along the muscle. If two levers 

 be made to rest on, or be suspended from, two points of such a 

 muscle placed horizontally, the points being at a known distance 

 from each other and from the point stimulated, the progress of the 

 contraction may be studied. It is found that the contraction 

 starting from the spot stimulated, passes along the muscle in the 

 form of a wave diminishing in vigour as it proceeds. The velocity 

 with which this contraction wave travels in the muscles of the 

 frog is about 3 or 4 metres a second ; and since it takes, in round 

 numbers, from about - 5 to *1 sec. for the contraction to pass over 

 any point of the fibre, the wave-length of the contraction wave 

 must be from about 200 to 400 mm. 



In the muscles of a mammal laid bare for the purposes of 

 experiment the velocity does not seem to be very different from 

 that in the frog; but in the intact muscles in their normal con- 



