GENERAL PHYSIOLOGY OF MUSCLE-TISSUE 67 



short time, augment the action of the muscle and give rise to the treppe 

 effect. (Lee.) In time, however, if the stimulation be continued, the 

 irritability declines, the height of the contraction diminishes and 

 finally the muscle ceases to respond to any stimulus. 

 Variations in the Temperature. The temperature at which all phases of 

 the contraction process, as represented by the myogram, attain their 

 physiologic maximum value is about 3oC. If the temperature 

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



FIG. 26. SINGLE CONTRACTIONS OF THE GASTROCNEMIUS MUSCLE AT DIFFERENT TEMPERA- 

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



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 4oC. to 5oC. 

 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. 26.) 



FIG. 27. CONTRACTIONS OF A GASTROCNEMIUS MUSCLE 

 WITH DIFFERENT LOADS. (Brodie.) 



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



weighted will not 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. 27, 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 

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

 of rising and falling energy. 



4. Rapidly Repeated Stimulation.Prolonged or excessive activity of our own 



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



