482 



OVERWEIGHTED MUSCLES. 



shock is stronger than the make. In fig. 327, B shows the effect produced by a 

 single break induction shock, and M that of a single make shock.] 



Overweighted Muscles. The foregoing remarks apply to curves obtained by a light lever 

 connected with the muscle. If the muscle lever be "overweighted '," or overloaded, i.e., if the 

 lever be loaded, so that when the muscle contracts it has to lift these weights, the course of the 

 curve varies according to the weight to be lifted. It is necessary, however, to support the lever 

 in the intervals when the muscle is at rest. As the weights are increased, the occurrence of the 

 contraction is delayed. This is due to the fact that the muscle, at the moment of stimulation, 

 must accumulate as much energy as is necessary to lift the weight. The greater the weight, the 

 longer is the time before it is raised. Lastly il (muscle n ay be so "loaded," or "overloaded," 

 that it cannot contract at all ; this is the limit of the miscular or mechanical energy of the 

 muscle (r. Helmhvltz). 



Fatigue. If a muscle be caused to contract so frequently that it becomes 

 l - fatigued" the latent period is longer, the curve is not so high, because the 



muscular contraction is less, 

 and the abscissa is longer, i.e., 

 the contraction is slower and 

 lasts longer (fig. 328). Cool- 

 ing a muscle has the same 

 effect. Soltmann finds that, 

 the fresh muscles of new-born 

 animals behave in a similar 

 manner. The myogram has 

 a flat apex and considerable 

 elongation in the descending 

 limb of the curve. 

 Contraction of a. fatigued frog's muscle writing its contrac- Constant Current. If the 

 tion on a vibrating plate attached to a tuning-fork. Each motor nerve of a muscle be 

 vibration = '01613 second ; a b = latent period ; b c stage stimu l a ted by a make or break 

 of increasing energy; c a, of decreasing energv. II, The , , - J . . 

 most rapid writing movements of the right hand inscribed shock ot a constant current, 

 on a vibrating plate. Ill, The most rapid trembling tetanic the resulting muscular con- 

 movements of the right fore-arm inscribed on the same traction corresponds exactly 

 P late - to that already described. If, 



however, the current be made or broken with the muscle itself directly in the 

 circuit, during the make shock, there is a certain degree of contraction which lasts 



for a time, so that the curve 

 assumes the form of fig. 

 329, where S represents the 

 moment of closing or making 

 the current, and the 



Fig. 329. 

 Effect on a muscle of closing and 

 S, closing ; O 



moment of opening or break- 

 opening a constant current. it / 336 D) 



opening shock ( Wundt). . . . ,-, , 



The investigations of Cash and 



Kronecker show that individual muscles have a special form of muscle-curve ; the omohyoid 



of the tortoise contracts more rapidly than the pectoralis. Similar differences occur in the 



muscles of frogs and mammals. The flexors of the frog contract more rapidly than the extensors 



(Griitzner) Sometimes within one and the same muscle there are "red " (rich in glycogen) and 



' ' pale " fibres ( 292). The red fibres contract more slowly, are less excitable, and less easily 



fatigued {Griitzner). The muscles of flying insects contract very rapidly, even more than 100 



times per second. 



Poisons. Very small doses of curara or quinine increase the height of the contraction 



(excited by stimulation of the motor nerve), while larger doses diminish it, and finally abolish 



it altogether. Guanidin has a similar action in large doses, but the maximum of contraction 



lasts for a longer time. Suitable doses of veratrin also increase the contractions, but the stage 



of relaxation is greatly strengthened (Rossbach and Clostermeyer). Veratrin, antiarin, and 



digitalin, in large doses, act upon the sarcous substance in such a way that the contractions 



become very prolonged, not unlike a condition of prolonged tetanus (Harlcss, 1862). The 



latent period of muscLs poisoned with veratrin and strychnin is shortened at first, and after- 



