414 



THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



Muscles owe their color to a peculiar red pigment (myochrome) which 

 is closely related to haemoglobin but does not agree with it spectroscopically 

 (K. A. H. Morner). 



3. STIMULATION OF MUSCLES AND OF NERVES 



A. THE MUSCLE CURVE 



1. Method. A, muscular contraction can be recorded in several ways which 

 differ in principle but which finally reduce to two groups, according as the short- 

 ening induced by the stimulus is allowed to take place or not. In the latter case 



FIG. 153. Apparatus of Fick for recording variations in the length and in the tension of a muscle 

 artificially stimulated. By unhooking the tension recorder the lever, HH , is allowed to move 

 freely up and down like an ordinary muscle lever. For further explanation, see text. 



the tension of the muscle increases as a result of the excitation, but its length 

 remains constant. For this reason such contractions are called isometric con- 

 tractions, and the variations of tension are recorded after Fick's method as 

 follows (Fig. 153). The muscle (M) is attached to a strong steel spring (f) 

 which bears a long writing point (/&) for magnifying and recording its move- 

 ments. When the muscle is stimulated, it attempts to bend the spring, but since 

 the latter yields but slightly, the muscle cannot shorten to any appreciable 

 extent; consequently the whole effect of the muscular activity is to increase the 

 tension. 



In the other method a lever loaded with a weight is commonly used, and 

 the weight is so chosen that the effort of the muscle to shorten when stimulated 

 is effective. The lever is lifted, therefore, and the resulting curve is a record 

 of variations in the length of the muscle during the contraction. 



