ALTERATION IN FORM DURING CONTliACTION. 49 



which must equal A ^ -h 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 

 elevation of the muscle when the weight id 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 apph'ed 

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

 b' B\ with the weight id. It therefore follows that the 

 extension cb' must be gi'eaterthan 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 5^^. This point 5^% 

 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.^ 



Yet another point of gi'eat interest is observable in 

 studying this alteration in the elasticity. When a cer- 

 tain weight, k, 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 

 * See Xotes and Ad'litions, No. 1. 



