436 



THE FUNCTIONS OF CROSS-STRIATED MUSCLES 



in which the muscle lifts a weight fastened directly to its free end, and the 

 projectile motion with dead iveights (Fick), where the muscle pulls on a lever 

 with balanced weights. 



In Figs. 173 and 174 are given examples of some of the different forms of 

 motion, namely: Fig. 173 a, an isotonic contraction, Fig. 173 ft, a simple pro- 

 jectile motion, Fig. 174, projec- 

 tile motions with dead balanced 

 weights. 



In curves approximately iso- 

 tonic, Fig. 173 a, as well as in 

 pure auxotonic curves, which 

 naturally reproduce the changes 

 in length of the muscle most ex- 

 actly, we find in the ascending 

 limb a break, which is not an 

 artifact but which, on grounds 

 that cannot be discussed here, is 

 probably due to the more slug- 

 gish contraction of the red mus- 

 cle fibers (cf. page 416). In the 

 projectile curve this irregularity 

 does not appear, at least not so 

 clearly, because the movement 

 of the lever does not record the 



finer details of the contraction. The contraction produced by a single stimulus 

 is, therefore, to a certain extent compound, owing to the fact that the different 

 kinds of fibers composing the muscle become active at different times. In an 

 exact analysis of muscular contractions, it is necessary to give this circumstance 

 its proper weight. 



Fig. 175 represents the single contraction of a muscle poisoned with vera- 

 trin, recorded on a slow-moving drum. Veratrin affects the red muscle fibers 



FIG. 173. Frog's gastrocnemius. a, isotonic con- 

 traction; b, simple projectile contraction. Both 

 were obtained with the same loads, 80 g., after 

 Santesson. 



FIG. 174. Frog's gastrocnemius. 1, loaded with 4 g., i. e., with the bare lever; 2, 40 g. dead 

 weight; 3, 100 g. dead weight; 4, 200 g. dead weight. 



so that they contract much more slowly than is normal. The first rapid curve is 

 referable to the white fibers, the second long-drawn-out curve to the red fibers. 



