

STRIATED MUSCLE. 85 



If a muscle be suspended vertically by one extremity, hav- 

 ing fastened to it at the other a pencil which makes a mark 

 upon a vertical cylinder revolving regularly, so long as 

 the muscle is under the first form a horizontal line will be 

 traced upon the cylinder. Should any excitant act upon the 

 muscle, it will still continue for a certain time to trace a 

 straight line, and this tracing will represent graphically the 

 period of latent excitation (Fig. 19, 1, 2, and 3, A B). As the 

 muscle passes into the second form, its lower extremity will 

 trace an ascending line (Fig. 19, BO), representing the pas- 

 sage from one form to the other ; at the level attained by 

 this line we shall find that a new horizontal line begins, 

 representing the time during which the second form lasts ; 

 finally will come a descending line, representing the return 

 to the first form (DE). The various instruments called 

 myographs are constructed on this principle (Helmholtz, 

 Marey) ; and in this way, also, have been obtained the 

 recorded writings of muscular contraction, with analysis 

 of the different periods. 



If we examine by this means the contraction of a muscle, 

 which follows a short and sudden irritation (a blow, for 

 instance), we find in the record that the descent immediately 

 follows the ascent (Fig. 19, 2, CD), which shows that the 

 second form has existed only for a short time, and is there- 

 fore represented, not by a line, but simply by a point, mark- 

 ing the passage from the ascent to the descent. This is 

 called the jerk, or muscular convulsion. But when short 

 and sudden excitations succeed each other rapidly, we see, 

 by the diagram, that a new contraction begins before the 

 descent of the first is finished (Fig. 19, 3, c, c', c", c'") ; that 

 is, the muscle, beginning to return to the first form, has been 

 again induced to take the second ; these half-descents, inter- 

 rupted by a new ascent, are therefore marked upon the dia- 

 gram by a series of undulating lines ; they approach nearer 

 the corresponding level of the second form, when these 

 excitations succeed one another more rapidly (Fig. 19, 3, line 

 F). We can easily conceive that the closer the excitations 

 follow each other, the shorter the undulations will be marked, 

 until at length they form a straight line, lasting as long 

 as the excitations continue to take place with the same 

 rapidity ; the muscle all this time will maintain the second 

 form. 



This preservation of the second form, considered as the 

 result of a succession of jerks (secousses) or continuous 



