128 EXTENSIBILITY, ELASTICITY, AND WORK OF MUSCLE [cH. XL 



We may now give the results of an actual experiment ; a muscle 

 was loaded with successive weights of 50, 100, 150, etc., grammes, 

 and its length carefully measured in centimetres. 



Load .... 50 

 Total extension . . 3'2 

 Increment of extension 



100 



150 



200 

 9-5 

 1-5 



250 

 10 

 0-5 



300 



10-3 



0-3 



in rigor 



In tetanus 



Normal 



Figure 156 shows that the contracted muscle is more extensible 

 than the uncontracted muscle. This may be still further illustrated 



by an example given on the opposite 

 page in the form of a diagram. 



The thick lines represent the con- 

 tracted muscle, the thin ones the un- 

 contracted. It is represented as being 

 stretched by different weights indicated 

 along the top line; and the lengths 

 under the influence of these weights 

 are separated by equal distances. 

 Thus A C represents the length of the 

 uncontracted muscle, A B of the con- 

 tracted muscle when unloaded. A' C' 

 and A' B' the same under the influence 

 of a weight of 50 grammes, and so on. 

 The curve connecting the ends of 

 the lengths of the contracted muscle 

 falls faster than that obtained from 

 the uncontracted one, until at the 

 point P under the influence of a weight 

 of 250 grammes, the two curves meet; 

 that is to say, 250 grammes is the 

 weight which the muscle is just un- 

 able to lift. Suppose a muscle has to 

 lift the weight of 200 grammes, it 

 begins with a length A" C", but when 

 it contracts it has a length A" B", that 

 is, it has contracted a distance of B" C", 

 which is very small; when it has to 

 lift a less weight it shortens more, 

 when a greater weight it shortens less ; till when it shortens least it 

 lifts the greatest weight. 



This experiment illustrates the general truth that when a muscle 

 is contracted it is more extensible. At the point P the energy 

 tending to shorten the muscle (its contractile power) is exactly equal 

 to the energy tending to lengthen it against its elastic force. Thus 

 we have the apparent paradox at this point that a muscle when 



Fatigued 



FIG. 150. Extensibility of muscle in 

 different states ; tested by 50 grammes 

 applied for short periods. Tracings 

 to be read from left to right. (After 

 Waller.) 



