52 EXPERIMENTAL PHYSIOLOGY 



load and b d the height of contraction, the work is represented by 

 o b x b d, i.e. by the rectangle obdk, and similarly for all the other 

 contractions. These rectangles are not, however, readily comparable ; 

 therefore proceed in the following manner. Determine the number of 

 grm. mms. of work performed in each contraction and divide this by 

 10 ; measure off on the squared paper a line equal to the number 

 obtained vertically under the contraction. Thus for the contraction 

 b d, the work was Job x b d grm. mms. = \ x 160 x 18 = 576. 

 Therefore a line b l 57-6 mm. was drawn as a continuation of d b. 

 Then complete the rectangle b l m n, which then contains 576 

 sq. mms., and therefore represents the total work performed, 1 sq. mm., 

 representing 1 grm. mm. of work. It will of course be f of the 

 rectangle o d. In a similar manner the other rectangles were drawn 

 and represent the other amounts of work for each contraction. The 

 aim of this has been to represent each successive work by rectangles 

 upon equal bases of 10 mm., and therefore the heights are a measure 

 of the work done and at once appeal to the eye. 



We see directly that the amount of work performed at first 

 increased rapidly as the load was increased, and reached a maximum 

 at a load of 160 g. From that point it decreased, but at a less rapid 

 rate than it had increased, and at 320 g, although the height of lift 

 was only § mm., the amount of work performed was considerable. At 

 360 g. the muscle only gave a scarcely perceptible lift. 



This experiment also gives us a means of determining one other 

 point in a muscle twitch, viz. the amount of load it is just able to lift 

 when it is stimulated. In order, however, to get comparable results it 

 is necessary to expresss this weight in a form for a definite amount of 

 muscle. As it depends directly upon the transverse sectional area of 

 the muscle, it is usual to express it in grams per sq. cm. of sectional area, 

 and it is then spoken of as the ' ABSOLUTE FORCE ' of the muscle. 



We may gain this approximately from the preceding experiment if 

 we know the length and transverse section of the muscle. In order to 

 obtain these, the weight, specific gravity, and length were measured. 

 These were : W = 329 g. S.G. = 1104, I = 2125 mm. The load it 

 was just unable to lift was 360 g. Its volume (r) is given by 



W "329 



- - = = -298 cub. cm. = 298 cub. mm. Therefore its average 



transverse section - = n . rt _ = 1402 sq. mm. Hence the absolute 

 L 21-25 



360 

 force per sq. mm. of transverse sectional area was = 25-6 grms. 



Hence the absolute force per sq. cm. of sectional area was 2,560 

 grams. 



