CHANGE OF FORM IX MUSCLE DURING ACTIVITY 



119 



it often happens that even with the most favourable conditions, 

 the strongest single induction shocks scarcely produce any visible 

 effect of excitation (contraction), while the same parts (intestine, 

 ureter, muscle of mollusc) are thrown into tetanus by the rapid 

 succession of stimuli from a vibrating Neff's hammer, at compara- 



FIG. 52. 



Fio. 53. 



Fics. 51-53. Muscle of Frog, indirect excitation with induction currents of increasing strength at 

 uniform frequency (10-12 per sec.) (Griitzner.) 



tively high coil frequency. With the constant current, too, it 

 may often be observed that with repeated closure at fairly short 

 intervals, a current ineffective in itself will gradually produce 

 effectual excitation (Engelmann). This property of summation 

 of stimuli characterises all irritable protoplasm (ciliated cells, 

 nerve cells, vegetable protoplasm, e.g. Dioncea, etc.) in a more or 



