78 PHYSIOLOGY OF MUSCLE AND NERVE 



Similar differences are exhibited by the red and pale muscles of the 

 rabbit, the soleus (red) contracting in 1.0 sec. and the gastrocnemius 

 (pale) in 0.2 sec. In winter the reaction-time of the muscles of cold- 

 blooded animals is much prolonged. Smooth muscle reacts very slug- 

 gishly, an ordinary contraction requiring as a rule from 10-20 sec. for 

 its completion. 



It is evident, therefore, that muscle tissue differs in its speed of 

 reaction and that this difference is dependent upon chemico-physical 

 peculiarities of its substance. We know that red muscle is a more 

 concentrated tissue than pale muscle and that it embraces a larger 

 amount of sarcoplasmic material. It seems, therefore, that the greater 

 water content of the latter exerts a favorable influence upon its 

 rapidity of action. The same holds true in the case of non- 

 striated and striated muscle. Inasmuch as the latter contains more 

 water and a smaller amount of undifferentiated sarcoplasm, its speed 

 of contraction must be much greater. 



FIG. 45. EFFECT OF CHANGES IN TEMPERATURE ON MUSCULAR CONTRACTION. 

 The temperature was raised 5 each time. 



Influence of Temperature. Warmth increases the power and 

 speed of reaction of this tissue, because it exerts a favorable influence 

 upon the chemical processes underlying muscular contraction. Hence, 

 a series of myograms recorded at gradually rising temperatures, usu- 

 ally shows a progressive increase in the height and corresponding de- 

 crease in the length of the different contractions. 1 At C., or rather, 

 a little below this point, 'the muscles of the frog lose their irritability 

 entirely. Consequently, if a muscle of this kind is stimulated at a 

 degree or two above freezing, it gives solely a very low and prolonged 

 contraction. If the temperature is now raised, say, three degrees at a 

 time, the individual contractions decrease in length but increase in 

 height. Beginning at about 9 C., their height is slightly decreased, 

 but again increased at about 18 C. A second maximum is reached 

 at 30 C. Subsequent to this point they again diminish in size until 



1 Gad and Heymans, Archiv fur Physiol., 1890, 59. 



