ALTERATION IN FORM DURING CONTRACTION. 49 



which must equal A B + c b' = A' b', in which A b is 

 the natural length of the active muscle when un- 

 weighted, and c b' is the extension which the active 

 muscle undergoes on the application of the same weight 

 p. A' B' A'b'=b' B' is, therefore, the height of 

 e^ vat ion of the muscle when the weight p is applied. 

 Now, our former experiments have shown that the 

 height of elevation decreases as the weight increases. 

 The height of elevation b B, when the weight applied 

 = o, is, therefore, greater than the height of elevation 

 b' B', with the weight p. It therefore follows that the 

 extension c b' must be greater than the extension d' B' ; 

 or, in other words, the same weight, p, extends the 

 ^muscle more when the latter is active than when it 

 is quiescent. Calculating on this principle the curves 

 of the extension of the active, as well as of the in- 

 active, muscle, for the first we find the curve b b' y ; 

 for the second the curve B B' x ; and these two con- 

 tinue gradually to approach each other, until they at 

 last cut each other at the point B iv . This point iv , 

 which corresponds with the weight p, shows that when 

 this weight is applied, the length of the active and 

 the inactive muscles is equal. If, therefore, when the 

 weight p is applied, the muscle is irritated, the height 

 of elevation is nothing. The muscle is incapable of 

 raising this weight, a fact which we have already noticed 

 in previous experiments. 1 



Yet another point of great interest is observable in 

 studying this alteration in the elasticity. When a cer- 

 tain weight, />;, is applied, the extension of the active 

 muscle = c' b" : that is, the active muscle, when this 

 weight is applied, assumes exactly the length proper to 

 1 See Notes and Additions, No. I. 



