348 THE OUTGO OF ENERGY 



contractions which at the beginning of the stim- 

 ulation period are marked by notches in the curve 

 fuse completely as longer stimulation brings on 

 fatigue. Here also the differences in the structure 

 of muscles already mentioned play an important 

 part. Thus the red muscles of the rabbit are 

 thrown into tetanus by a much smaller number 

 of stimuli per second than are the more quickly 

 contracting white muscles. 



Relation of Shortening in a Single Contraction 

 to Shortening in Tetanus. 1. Eecord side by 

 side the contractions of a muscle unloaded except 

 by the muscle lever. Stimulate with a single 

 maximal induction current; stimulate with a 

 brief tetanizing current. 



The shortening of the single twitch of the un- 

 loaded muscle is as great as the shortening in 

 tetanus. 



2. Load the muscle with ten grams and repeat 

 Experiment 1. 



The shortening in tetanus will now be con- 

 siderably greater than that of the single twitch. 



3. Load the muscle with ten grams but sup- 

 port the weight by the after-loading screw, so 

 that the weight cannot pull on the muscle until 

 the contraction begins. Kecord one contraction 

 on a stationary drum in response to a maximal 

 make induction current. Turn the drum one 



