118 CHANGE IN FORM IN A MUSCLE WHEN IT CONTRACTS [CH. X. 



tion is much more prolonged ; the latent period gets longer ; the period of 

 contraction gets longer ; and the period of relaxation gets very much longer ; there 

 is a condition known as contracture, so that the original base line is not reached by 

 the time the next stimulus arrives. In the last stages of fatigue, contracture 

 passes off. 



4. Effect of temperature. Cold at first increases the height of contraction, then 



FIG. 147. Effect of temperature on a single muscular contraction; N, normal; H, warm; (71, cooling 

 C2, very cold ; P, point of stimulation. The above tracing is a considerably reduced facsimile of a 

 tracing taken with the pendulum myograph. 



diminishes it ; otherwise the effect is very like that of fatigue increasing the 

 duration of all stages of the curve. 



Moderate warmth increases the height and diminishes the duration of all stages 

 of the curve, latent period included. This may be readily shown by dropping some 

 warm salt solution* on to the muscle before taking its curve. Too great heat 

 (above 42 C.) induces heat rigor due to the coagulation of the muscle proteids. 



5. Effect of veratrine. If this is injected into the frog before the muscle-nerve 

 preparation is made, the very remarkable result seen in the next diagram is 



FIG. 148. Veratrine curve, taken on a very slowly-travelling fcylinder ; the time tracing indicates 



seconds. 



produced on stimulation ; there is an enormous prolongation of the period of relaxa- 

 tion ; marked by a secondary rise, and sometimes by tremors. After repeated 

 stimulation this effect passes off, but returns after a period of rest. 



The Muscle- Wave. 



The first part of a muscle which contracts is the part where the 

 nerve-fibres enter ; but nerve impulses are so rapidly carried to all 

 the fibres that for practical purposes they all contract together. 

 But in a nerveless muscle, that is one rendered physiologically nerve- 



* Physiological saline solution used for bathing living tissue is a 07 to 0'9 per 

 cent, solution of sodium chloride in ordinary tap water, 



