GENERAL PHYSIOLOGY OF MUSCLE-TISSUE. 



67 



state known as galvanotonus; on opening the circuit at o the muscle again con- 

 tracted, after which it gradually relaxed and returned to its original 

 condition. The record shows also that during the actual passage of the cur- 

 rent the muscle substance was being stimulated by it. 



The Work Accomplished by a Muscle during the Time of a Single 

 Contraction. By work is meant the overcoming of opposing forces. 



FIG. 30. MYOGRAH DUE TO THE ACTION OF A GALVANIC CURRENT, APPLIED DIRECTLY TO A 

 MUSCLE, WHEN THE CIRCUIT WAS CLOSED (c) AND WHEN IT WAS OPENED (o). 



In the physiologic activities of the body the muscles at each contraction not 

 only overcome the resistances of antagonistic muscles, the weight of the 

 limbs, the friction of joints, etc., but in addition overcome various external 

 resistances connected with the evironment e.g., gravity, cohesion, friction, 

 elasticity, etc. The muscles may therefore be regarded as machines for 

 the accomplishment of work. Experimentally the work done by an iso- 

 lated muscle maybe calculated if the height of the contraction is first obtained 

 and then multiplied by the weight 

 raised. The influence of the 

 weight on the height of the con- 

 traction is shown in Fig. 31, in 

 which only the height of the con- 

 traction or the degree of shorten- 

 ing and hence the lift of the weight 

 is represented. From this tracing 

 it will be observed that the extent 

 to which a muscle will shorten in 

 response to a maximal stimulus 

 is greatest when it is unweighted; 

 but as weights differing by a com- ^ _ TRACING SHOWING THE GRADUAL 

 mon increment are added, the DIMINUTION IN THE HEIGHT OF THE CONTRAC- 

 height of the contraction dimin- TION AS THE WEIGHT WAS INCREASED BY A COM- 



ishes until with a given weight it MON INCREMENT OF I0 GRAMS FROM T0 l8 



GRAMS. MAGNIFICATION OF THE LEVER, 4- 



IS ml. 



A careful study of the results of this experiment will show that the 

 work done gradually increased as the load was increased from o to 70 

 grams, when it amounted to 210 gram-millimeters; but that after this, 

 even though the weight lifted was greater, the height to which it was lifted 

 was less, and hence the work done gradually decreased, until it amounted 

 to nothing. 



The following table will also show the work done by a frog's muscle 

 according to Rosenthal. 



