26 THE PHYSIOLOGY OF MUSCLE AND NERVE. 



DURATION OF A SIMPLE MUSCULAR CONTRACTION. 



Insect 0.003 sec. 



Rabbit (Marey) 0.070 " 



Frog 0.100 " 



Terrapin LOOO " 



The series may be continued by the figures obtained from the 

 plain muscle, thus: 



The involuntary muscle (mammal) 10.00 



Foot muscle of slug* (Ariolimax) 20.00 



The duration of the simple contraction varies considerably 

 in the muscles of different parts of the same animal. Thus, 

 according to Cash, the hyoglossal muscle in the frog requires 

 0.205 to 0.3 second, while the gastrocnemius takes 0.12 second; 

 in the tortoise the pectoralis major requires 1.8 seconds, the 

 omohyoid only 0.55 second; in the rabbit the soleus (a red 

 muscle) requires 1 second, the gastrocnemius (a pale muscle) 

 0.25 second. On examining into these differences it may be 

 shown that the variations bear a relation to the special functions 

 of the muscles. Where rapid movements are requisite or advan- 

 tageous the muscle shows the property of quick contraction and 

 relaxation, while in other places, in which maintenance of con- 

 traction is the more important feature, the properties of the 

 muscle have been developed so as to adapt them to this kind of 

 contraction. The skeletal and the plain muscles exhibit the 

 extreme examples in this form of adaptation. 



The Curve of Contraction. — When a contracting muscle is 

 attached to a lever this lever may be made to write upon a smoked 

 surface and thus record the movement, more or less magnified 

 according to the leverage chosen. If the recording surface is sta- 

 tionary the record obtained is a straight line and indicates only the 

 extent of the shortening. If, however, the recording surface is in 

 movement during the contraction the record will be in the form of a 

 curve, which, making use of the system of right-angled co-ordinates, 

 will indicate not only the full extent of the shortening, but also 

 the amount of shortening or subsequent relaxation at any moment 

 during the entire period. To obtain such records from the rapidly 

 contracting frog's muscle it is evident that the recording surface 

 must move with considerable rapidity and with a uniform velocity. 

 A curve of this kind is represented in Fig. 8. C represents 

 the axis of abscissas and gives the factor of time. A vertical 

 ordinate erected at any point on C gives the extent of shortening 

 at that moment. Below the curve of the muscle is the record 

 of the vibrations of a tuning fork giving 100 double vibrations 

 per second; that is, the distance from crest to crest represents an 

 * Carlson, "American Journal of Physiology," 10, 418, 1904. 



