GENERAL PHYSIOLOGY OF MUSCLE AND NERVE. 



99 



If one moves a pencil vertically up and down on a piece of paper, a straight 

 line is written ; if while the vertical movements are continued the paper be 

 drawn along at a regular rate in a direction at right angles to the move- 

 ment of the pencil, a curve will be traced. If the paper be moved at a regular 

 rate, the shape of the curve will depend on the rate at which the pencil is 

 moved, and, if the speed of the paper be known, the rate of movement of the 

 pencil can be readily determined. This principle is employed in recording the 

 movements of muscles. The muscle is connected with a mechanism which 

 rises and falls as the muscle contracts and relaxes, and records the movement 

 of the muscle on a surface which passes by the writing-point at a regular 

 speed (see Fig. 35) ; such a record is called a myogram. 



The Myograph. The writing mechanism, together with the apparatus 

 which moves the surface on which the record of the movement of a contracting 

 muscle is taken is called a myograph. The writing mechanism has usually the 

 form of a light, stiff lever, which moves very easily on a delicate axis ; the 

 lever is so connected with the muscle as to magnify its movements. The point 

 of the lever rests very lightly against a glass plate, or surface covered with 

 glazed paper, which is coated with a thin layer of soot. The point of the lever 

 scratches off the soot, and the movements are recorded as 

 a very fine white line. At the close of the experiment 

 the record is made permanent by passing it through a 

 thin alcoholic solution of shellac. The recording surface 

 in some cases is in the form of a plate, in others of a cyl- 

 inder, and is moved at a regular rate by a spring, pendu- 

 lum, falling weight, clockwork, electric or other motor. 1 



The record which is traced with the myograph lever 

 by the muscle has the form of a curve. From the height 

 of the curve we can readily estimate the amount that 

 the muscle changes its length, but in order to accu- 

 rately determine the duration of the contraction process 

 and the time relations of different parts of the curve, 

 it is necessary to know the exact rate at which the 

 recording surface is moving. The shape of the curve 

 drawn by the muscle will depend very largely on the 

 rate of the movement of the surface on which the record 

 is taken. This is illustrated by the four records repro- 

 duced in Figure 33. These were all taken from the 

 same muscle within a few minutes of each other and 

 under exactly the same conditions, except that in the 

 successive experiments the speed of the drum on which 

 the record was traced was increased. 



A glance at these records shows that a knowledge 

 of the rate of movement of the surface on which the record is taken is indis- 

 pensable to an understanding of the time relations of the different parts of the 

 1 See O. Langendorff ; Physiologische Graphik, Franz Deuticke, Leipzig, 1891. 



FIG. 33. Records of four 

 contractions of a gas- 

 trocnemius muscle of a 

 frog: a, recording sur- 

 face at rest; 6, surface 

 moving slowly; c, sur- 

 face moving more rapidly ; 

 d, surface moving even 

 faster. 



