32 EXPERIMENTAL PHYSIOLOGY 



the point of stimulation. Then take the following curves on this 

 abscissa : 



1. A simple muscle curve at the room temperature. 



2. A simple curve after warming the muscle by dropping Ringer's 

 solution, warmed to about 30 C., upon the muscle. 



3. A simple curve after cooling the muscle by dropping upon it 

 ice-cold Ringer. 



Finally, take a time tracing below the abscissa. 



FIG. 35. Method of studying isometric contraction, sp, Spiral spring ; 

 s, screw for regulating its tension. 



Notice the effect of heat and cold respectively upon the period of 

 latency and upon the amount and duration of the contraction. 



Isometric contraction. If the contracting muscle is prevented 

 from shortening, or allowed only to shorten to so small an extent so 

 that it practically remains of the same length throughout, the con- 

 traction is said to be isometric. It is recorded by attaching the muscle 

 very close to the fulcrum of the muscle lever, which is held down by 

 a strong spiral spring (Fig. 35) instead of by a weight. All the other 

 arrangements of the experiment are the same as with the ordinary 



