GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 67 



physiologic maximum value is about jbC. If the temperature 

 of the muscle falls to 2oC. there is a corresponding decline in activity, 

 as shown by an increase of the latent period, a decrease in the height 

 of curve i.e., in the shortening of the muscle an increase both in 

 the contraction and relaxation periods. As the temperature approaches 

 oC, the height of the curve again suddenly increases, indicating, for 

 some unknown reason, an increase in the irritability. This is, however, 

 scarcely a physiologic condition. At a temperature of 40 C. to 50 C. 



FIG. 25. SINGLE CONTRACTIONS OF THE GASTROCNEMIUS MUSCLE AT DIFFERENT TEMPERA- 

 TURES. Time tracing 200 per second. (Brodie.) 



the muscle suddenly contracts and passes into the condition of heat 

 rigor or rigor caloris. The protein constituents of the muscle are 

 coagulated and the irritability destroyed. (Fig. 25.) 



3. Variations in the Load. The extent to which a muscle is loaded or 

 weighted will riot only determine the height of the contraction, but also 

 the time relations of all its phases. This is apparent from an exami- 

 nation of Fig. 26, in which it is shown that with an increase in load 

 there is a decrease in the height of the contraction, an increase in the 



FIG. 26. CONTRACTIONS OF A GASTROCNEMIUS MUSCLE 

 WITH DIFFERENT LOADS. (Brodie.) 



latent period, and a general increase in the duration of both the periods 

 of rising and falling energy. 



Rapidly Repeated Stimulation. Prolonged or excessive activity of our own 

 muscles is accompanied by a feeling of stiffness or soreness and lassi- 

 tude. There is at the same time a diminution in the speed and vigor 

 of the contractions and the power of doing work. To this condition 

 the term, fatigue has been given. The cause of the fatigue is attributed 

 to a diminution in the amount of the energy-yielding compounds as 



