ANATOMY AND PHYSIOLOGY OF NERVOUS SYSTEM. 



GG5 



nerve. The normal excitant is the physiological stimulus; it is the 

 will. It originates within the nerve-centers, from where it is trans- 

 mitted to the motor nerve. Any stimulus when applied to a nerve 

 causes the molecules in that localized area to vibrate and so produce 

 certain electromotive changes. By the changes set up in this par- 



Fig. 267. Schema of Apparatus for the Study of the Law of Con- 

 tractions in the Frog. (LAHOUSSE.) 



P, Daniell cells. C, Pohl's commutator. E and E, unpolarizable electrodes 

 applied to sciatic nerve. R, Rheocord. 



icu^ar area of nerve, the contiguous parts are also necessarily 

 >rought into activity by reason of nerve-conduction. By many 

 uithors this transmission of changes along the course of the nerve so 

 to act as excitants is known as the true physiological stimulus, 

 ms, the vibrations in each segment perform the function of exci- 

 mt for each succeeding segment. 



