CHAPTER IV. 

 PHYSIOLOGY OF NERVE. 



All protoplasm possesses the fundamental property of irrita- 

 bility, i.e., it can be influenced by external stimuli and the effect 

 of such stimuli can be transmitted to parts at a distance from the 

 point of application. In animals one kind of tissue has developed 

 this property to a marked degree, namely nervous tissues. Con- 

 duction of the impulse aroused by stimulating a nerve is so rapid 

 that through the mediation of the nervous system, integration of 



the organism is brought 

 about. The animal acts as 

 a unit not as a composite 

 of unrelated parts. Nerve 

 fibres are similar to the 

 ~^ wires of a telegraph system 



which connect the different 

 parts of a country with 



FIG. 13. Dissection of the frog's gracilis muscle , t u p llt t u p wl ' rP c 



to demonstrate that a nerve conducts in both direc- eacn Otner. ^UL ^ WIT 

 tions. Stimulation at (a) will cause contraction of j i 



both(a)and(&)orru*wrjo. and communication be- 



tween parts is lost. Cut 



the nerves to an organ and it loses its coordination with the rest 

 of the body. 



Just as in a wire so in a nerve fibre, conduction can take place 

 in both directions. This can be shown by means of a galvano- 

 meter. Stimulation of a fibre in the middle of its course will 

 cause a deflection of a galvanometer no matter at which end it is 

 placed. The following experiment also proves the truth of the 

 statement. 



Experiment 18. Kuehne's gracilis experiment. Expose the 

 inner surface of a gracilis muscle in a frog. It will be seen that 

 the two portions of the muscle are fed by branches of the same 

 nerve. Separate the two parts of the muscle without injury 

 to the nerves. It is possible to do this so that the nerve is the 

 only connection between the two parts (Fig. 13). 



46 



