6 4 8 



A MANUAL OF PHYSIOLOGY 



the effect of cold in strengthening the beat is often very marked. 

 Temperature affects the contraction ^curve of smooth muscle much 

 in the same way asjthat of striated muscle (Fig. 234). Up to 40 C. 



there is an increase in the 

 height and a diminution in 

 the length of the curve. 

 Above that temperature the 

 height is diminished. The 

 latent period is markedly 

 diminished by heat (from 

 3' 5 seconds at 10 C. to 

 0*2 seconds at 40 C). 

 (C. C. Stewart). 



(c) Influence of Previous 

 Stimulation Fatigue. If 

 a muscle is stimulated by 



R ^ S 



FIG. 235. AUTOMATIC MUSCLE INTERRUPTOR. 



K, battery; P, primary ; S, secondary coil: a series of equal shocks 

 Hg, mercury cup. thr()wn ^ ^ ^^ in _ 



tervals, arid the contrac- 

 tions recorded, it is seen that 

 at first each curve overtops its 

 predecessor by a small amount. 

 This phenomenon, which is 

 regularly observed in fresh 



FIG. 236. FATIGUE CURVE OF MUSCLE: 

 FROG'S GASTROCNEMIUS. 



The arrangement with which the 

 curve figured was obtained was a so- 

 called automatic muscle interrupter 

 (Fig. 235). A wire on the lever is made 

 to close and open the primary circuit 

 of an inductorium, the muscle or nerve 

 being connected with the secondary. 

 Every time the needle touches the 

 mercury the muscle is stimulated auto- 

 matically. Another arrangement is 

 shown in Fig. 237. 



FIG. 237. AUTOMATIC MUSCLE 

 INTERRUPTOR. 



A, femur with gastrocnemius at- 

 tached, supported in clamp ; C, metal 

 hook with fine wire attached to lever F. 

 The wire is continued along the lever 

 and connected with a sewing-needle, the 

 point of which just dips into the mercury 

 cup D. A wire from one pole of the 

 Daniell cell E dips permanently into the 

 mercury ; the wire B from the other pole 

 is attached to the upper end of the 

 muscle or the clamp. 



skeletal muscle (Fig. 238), although it was at one time supposed 

 to be peculiarly a property of the muscle of the heart (Fig. 239), 

 is called the 'staircase,' and seems to indicate that within limits 



