548 



PHYSIOLOGY. 



of the curve represents the contraction of the muscle until it has 

 reached its maximum. The rate of contraction is at first a trifle 

 slow, then more rapid and more slow a second time. The extent is 



V 



a second. 



Relaxation Period. After the muscle has contracted to its max- 

 imum, it begins to relax at first slowly, then more quickly, and 

 finally more slowly again. Its duration is 5 / 100 of a second. It is 

 shorter with a weak stimulus and longer with a strong stimulus. 



Fig. 192. Arrangement of Apparatus in Conducting Experiments on 

 Nerve and Muscle. (STIRLING.) 



B, Galvanic battery. K, Electric key in primary circuit. P, Primary coil 

 of induction machine. 8, Secondary coil of induction apparatus, from which 

 the current is conducted when the key (A'') is open to the electrode (E) on 

 which" rests the nerve (n). The muscle (M) is supported by a clamp under 

 a glass shade, its tendon being connected by a thread with a lever (L) writ- 

 ing on the smoked surface of a revolving drum. The time-marker (TM) is 

 included in the primary circuit so that when the current passes through P by 

 closing the key (K) it also traverses the electromagnet of the time-marker 

 and causes a record of the instant of stimulation to be made on the surface 

 of the drum. S, Stand supporting moist chamber. W, Weight by which muscle 

 is stretched and which is lifted in the contraction of the muscle. 



In the myograph we use a light lever and a weight as near its 

 axis as possible to record the contraction. Here the tension of the 

 muscle in its contraction and relaxation remains nearly the same. 

 This contraction is called an isotonic contraction. The isometric 

 contraction is produced when the muscle pulls against a spring. 

 Here the muscle undergoes slight change in length and the energy 

 of change of form is transformed into tension and stored in the 

 spring. An examination of isometric and isotonic curves proves that 

 a muscle which has shortened to a given length will be making a far 



