374 TETANUS. 



those shown in Fig. 284 will be obtained. When the muscle is 

 at rest and unloaded, the recording point of the lever describes 

 the straight line o, x. The sudden application and speedy re- 

 moval of the load produces the curve .r, a, the muscle in this 

 instance failing to return to its original length. On being 

 tetanized, the muscle shortens from the level of x' a to the 

 level of o; and the application of the same load as before pro- 

 duces the long curve o' a'. 



Obs. VIII. Dicing contraction there is a diminution, a nega- 

 tive variation, of the natural muscle current. 



This is shown by the galvanometer (see Chap. XXV., 

 Sec. II.). 



It may also be shown by using the variations in the mus- 

 cular current as a means of stimulating a nerve supplying 

 another muscle. 



Get ready two nerve-muscle preparations as irritable and as 

 little injured as possible; one may be the whole of the under 

 Icir, with the femur cut off close to knee, and as long a sciatic 

 nerve as possible (Fig. 285 A); the other should include the 

 muscles of the thigh as well, the skin being in both cases re- 

 moved (Fig. 285 B). 



Place B on a glass plate, and let the extreme (central) end 

 of the nerve rest on a pair of electrodes connected with an in- 

 duction coil. 



Lay the nerve of A over the muscles of the thigh of B, as in 

 the figure. 



Send a single induction shock through B; there will be a 

 single contraction of the muscles of B, and almost at the same 

 time a single contraction of the muscles of A. 



Send an interrupted current through the electrodes of B. 

 The muscles of B will be thrown into tetanus. So also will 

 those of A. 



The single contraction of the muscles of B causes a single 

 variation in the natural currents of the muscles of B; this acts 

 as a single stimulus to the nerve of A, and so causes a single 

 contraction in the muscles of A. 



When the muscles of B are thrown into tetanus, each con- 

 stituent contraction of which that tetanus is made up causes a 

 corresponding variation in the natural current, which therefore 

 during the tetanus is undergoing a succession of variations. 

 Kach such variation acts as a stimulus to the nerve of A, and 

 accordingly the muscles of A are thrown into a tetanus, the 

 constituent contractions of which correspond exactly with 

 those of the muscles of B. 



In the galvanometer we have no such series of variations in 

 the position of the needle; the negative variation during teta- 

 nus appears as a steady backward swing of the needle. This 



