CAUSES AND PHENOMENA OF MOTION. 



29 



BECORD OF MUSCULAR CONTRACTION UNDER STIMULI. 



The muscles of the frog are those which can most conveniently be 

 experimented with and their contractions recorded. The frog is pithed, 

 that is to say its central nervous system is entirely destroyed by the inser- 

 tion of a stout needle into the spinal cord and the parts above it. One of 

 its lower extremities is used in the following manner. The large trunk of 

 the sciatic nerve is dissected out at the back of the thigh, and a pair of 

 electrodes is inserted behind it. The tendo-achillis is divided from its 



FIG. 280. Arrangement of the apparatus necessary for recording muscle contractions with a 

 revolving cylinder carrying smoked paper. A, revolving cylinder; B, the frog arranged upon a cork- 

 covered board which is capable of being raised or lowered on the upright, which also can be moved 

 along a solid triangular bar of metal attached to the base of the recording apparatus the tendon of 

 the gastrocnemius is attached to the writing lever properly weighted by a ligature. The electrodes 

 from the secondary coil pass to the apparatus being, for the sake of convenience, first of all brought 

 to a key. D (Du Bois Reymond's): C, the induction coil; F, " 



one); E, the key (Morse's) in the primary circuit. 



the battery (in this figure a bichromate 



attachment to the os calcis, and a ligature is tightly tied round it. This 

 tendon is part of the broad muscle of the thigh (gastrocnemius) which 

 arises from above the condyles of the femur. The femur is now fixed 

 to a board covered with cork, and the ligature attached to the tendon is 

 tied to the upright of a piece of metal bent at right angles (Fig. 280, B), 

 which is capable of movement about a pivot at its knee, the horizontal 

 portion carrying a writing lever (myograph). When the muscle con- 

 tracts the lever is raised. It is necessary to attach a small weight to the 



