GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



81 



its attendant phenomena is shown by an excised frog muscle 

 when stimulated for a long period of time by induction shocks 

 at intervals of one second. In a variable period of time the 

 muscle shows an increase in the duration of the latent period, 

 a diminution of the height of the contraction, in the power of 

 doing work, and an increase in the time required for relaxation. 

 If the stimulation continues, the contractions gradually decline 

 as the muscle becomes exhausted. (See Fig. 29.) 



FIG. 29. FATIGUE CURVES. EVERY TWENTIETH CONTRACTION RECORDED. 



5 . Nutrition. The irritability of a muscle which conditions the con- 

 traction process is dependent on the maintenance of its nutrition ; 

 hence a continuous and sufficient supply of nutritive material 

 and a rapid removal of waste products are essential conditions 

 for the exhibition of normal contractions. A diminution of 

 blood-supply or an accumulation of waste products sooner or 

 later impairs the irritability and diminishes the vigor and extent 

 of the contraction. Various drugs e. g., veratrin, barium, etc. 

 introduced into the circulation and finding their way into the 

 muscle modify the contraction process, as shown by a very great 

 increase in the duration of the relaxation period. 

 The Isometric Myogram. With the object of obtaining a 

 curve of the increase and de- 

 crease in the tension of a muscle 

 during a single contraction, with 

 the exclusion as far as possible 

 of a change in length, the muscle 

 may be made to contract against a 

 strong spring or similar resistance 

 sufficient to practically though 

 not absolutely prevent shorten- 

 ing. To this method the term 

 isometric has been given, and the FIG. 30. a. DIAGRAM OF ISOTONIC; b, 

 curve so obtained an isometric OF ISOMETRIC MUSCLE CURVES. 



myogram or a tonogram. The 



recording portion of the lever is prolonged some distance so that the 

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