THE MECHANICAL RESPONSE. 



359 



that no further augmentation of effect can be gained by the same 

 method. 



The height to which the free end of the muscle is raised when con- 

 tracting under isotonic conditions (which may be conveniently de- 

 signated the lift), obviously depends on the load. If, as before, we 

 measure the load in grammes and the lift in mm., and multiply the 

 one by the other, we have the work done during the shortening of the 

 muscle. 



To investigate the relation of load to lift, we cause the muscle to inscribe 

 a succession of curves, the load being increased by an equal amount after each 

 inscription, in such a way that the corresponding points in all the curves are in 

 the same vertical line, as shown in Fig. 193. As the attached (upper) end of the 



Fio. 193. 



FIG. 193. Series of isotonic curves with increasing load. The number to each curve 

 indicates the weight on the muscle in grammes. The broken line represents the 

 first part of an inertia curve, taken with the same muscle with a load of 10 grms. 

 See p. 360. After Tick. 



FIG. 193A. "Work-diagram (to be read from right to left) for the same muscle as it 

 would be if the tension were a fraction of the length of the muscle at any 

 particular moment after the beginning of the contraction. Diminution of 

 length is expressed by the distance from b, in the base line b a, to the foot of 

 the vertical line, of which the height expresses the corresponding tension. 

 Both figures have been reduced in the same proportion. In the original, 1 grm. 

 of tension was represented by 0*5 mm. After Fick. See Note 1. 



muscle is in the same position throughout, the writing lever attached to the 

 free end takes a lower position in the successive curves, the difference between 

 the base lines of the curves expressing the increase of length which the 

 additional load has produced. In the series of isotonic contractions of which 

 the curves are given in the figure, the loads and lifts were respectively as 

 follows : 2 



Loads (in grms. ) 

 Lifts (in mm. ) . 

 Products (grm. -mm.) 



5 10 

 . 23-5 23-5 

 . 117'5 235 



20 



22-0 



440 



30 40 



20-5 19-0 



615 760 



50 

 18-5 

 925 



60 70 

 17-5 16'5 

 1050 1155 



1 The reader will understand this diagram (Fig. 193A) more easily if he imagines it 

 placed on Fig. 193 with the base line vertical, and b on the beginning of the broken line. 



2 Fick, op. cit., S. 112. 



