71 



CHAPTEE VI 



THE THICKENING OP A MUSCLE ON CONTBACTION. 

 THE MUSCLE WAVE. 



When a muscle shortens during a twitch it also thickens, and this 

 thickening may be studied in the following experiment, whose object is 

 to magnify and record the changes in a transverse diameter at some 

 convenient spot. 



Experiment 1. — Take a tracing of the thickening- of a muscle during a 

 contraction by means of the apparatus shown in fig. 66. Arrange the apparatus 



Fig. 66. — Method or Kecording the Thickening of a Muscle as it Contracts. 



in the same way as for a simple twitch, but use the recording apparatus 

 shown in the figure. Make a gastrocnemius preparation from a curarised 

 frog, 1 and to its tendon attach a length of indiarubber, R. The muscle 

 is laid upon a narrow wooden support, h, whose upper surface is covered 

 with cork. The upper end is fixed to this base by two pins, to which two 

 fine wires are soldered, thus forming a pair of electrodes. The end of the 

 strip of rubber is pinned down to the cork base by a pin, so as to put the 

 muscle slightly on the stretch. Resting on the muscle at a point near the 

 electrodes is a light wire of aluminium, w, in the form of a hoop, the part 

 touching the muscle being hammered out flat. This wire is connected 

 below to a recording lever, l. 



1 The frog is previously curarised in order to prevent excitation of the muscle 

 through its nerve (see pp. 76, 77). 



