VOLUNTARY MUSCLE. 25 



contracts a record will be made on a drum. These levers are so 

 adjusted that they write directly one above the other. If both 

 parts of the muscle contracted simultaneously the levers would 

 move simultaneously. One end of the muscle is stimulated with 

 a single shock. That end contracts some time before the other, 

 as shown by the records upon the kymograph. By measuring the 

 length of muscle between the levers and determining the time 

 with a tuning fork on the drum, the rate in meters per sec. can be 

 ascertained. 



Relaxation is an active process and is not entirely due to the 

 effect of tension upon a muscle which has ceased to contract. 



If a frog's muscle is carefully isolated and dipped in olive oil 

 to reduce friction, it will actively relax after contraction, provided 

 it is floated on mercury. 



Volume of a Contracting Muscle. The contraction of a 

 muscle does not change its volume as the following experiment 

 will show. 



*Experiment 7. Two well insulated wires from the secondary 

 terminals of an inductorium are passed through one hole of a 

 rubber stopper. The bare ends of the wire are connected to 

 opposite ends of a frog's gastrocnemius, which is then suspended 

 within a wide-mouthed bottle. The hole through which the 

 wires passes is made water-tight. A glass tube drawn out to a 

 capillary is inserted in the other hole after the bottle has been 

 completely filled with isotonic NaCl solution. The solution 

 should extend a short distance into the capillary portion of the 

 tube. The inductorium is arranged to produce a tetanizing 

 current. In spite of the short-circuiting through the solution, 

 if a sufficiently strong current is used, the muscle can be made 

 to contract. 



Determine whether or not any change in volume takes place 

 due to contraction. 



Isotonic Contraction. When a muscle lifts a light load it 

 shortens with little opposition, the tension remaining nearly con- 

 stant throughout. Such a contraction is literally one with constant 

 or iso-tension, hence called isotonic. 



Experiment 8. Isotonic Muscle Contraction. The time 

 elements in the contraction and relaxation of a muscle can best 



