ADVANCED EXPERIMENTAL PHYSIOLOGY 115 



The previous experiment on the polarisation of electrodes should 

 be repeated with the unpolarisable electrodes. The result will be 

 negative if the electrodes have been well and truly made. 



CHAPTER XI 



TRANSMISSION OF A NERVOUS IMPULSE IN BOTH 

 DIRECTIONS 



The excitatory state produced by stimulation of a nerve can be 

 transmitted in both directions. This can be shown by the following 

 experiments. 



Sartorius Experiment. The sartorius muscle lies on the ventral 

 surface of the thigh (Eig. 31) and its outlines can be made distinct 

 by sponging it with the frog's heart full of blood. The muscle is 

 dissected out and its iliac end is divided into two portions (Fig. 113). 

 Stimulation with a weak induction shock at (a) or (a'), when there 

 are no nerve-fibres, will produce a contraction of the one half of the 

 muscle. Excitation, however, at (6) or (6'), where there are nerves, 

 will evoke a contraction of both halves. 



Gracilis Experiment. The gracilis muscle 

 of the frog is in two portions completely 

 separated by a tendinous intersection 

 (Figs. 31, 114). Both halves of the 

 muscle are supplied by a single nerve, the 



FIG. 113. Diagram of the 

 sartorius experiment to show 

 the transmission of a nervous 

 impulse in both directions. 



FIG. 114. Diagram of the 

 gracilis experiment to show the 

 transmission of a nervous im- 

 pulse in both directions. 



individual fibres of which divide and supply both halves of the 

 muscle. Stimulation of any kind at (a) or (a'), where there are no 

 nerve-fibres, causes only the corresponding half of the muscle to 

 contract ; but excitation at (6) or (6'), where the nerves lie, will 

 cause both halves to contract. 



