184 MUSCLE AND NERVE 



In nerves it may be demonstrated by Kuehne's experiment 

 on the sartorius of the frog. The end of the muscle, after being 

 slit longitudinally for a small distance, is stimulated at one tip, 

 which causes contraction of both tips. Cross-conduction be- 

 tween muscle fibers being impossible, the impulse generated 

 in the nerve fibers of one tip must pass back to other branches 

 of the same nerve fiber, and thus excite the other tip. A 

 similar experiment may be made on the electrical organ of 

 Malapterurus. The anterior roots of spinal nerves which 

 contain fibers transmitting normally in only one direction may 

 be shown to transmit also in the opposite direction by means 

 of the electrical change accompanying a nerve impulse. 



The rate of conduction varies in different tissues, and is 

 roughly related to the function. In muscles all gradations are 

 to be found, from the 0.02 to 0.03 meter per second of the smooth 

 muscle fibers of the rabbit's ureters to the 10 or 13 meters per 

 second in human muscle. The rate in nerves may be put at 

 27 meters per second in frogs and 35 meters per second in man. 

 The conduction process sweeps over irritable tissue in the form 

 of a wave, which in muscle is about 300 mm. long, while in 

 nerves it varies from 18 to 140 mm. in length. Conduction is 

 influenced by the same factors that affect contractility. 



Nature of Nerve Impulse. The nature of the process has not 

 been determined, but must be either of physical or chemical 

 character. The balance of evidence, at present, seems to favor 

 the view of its chemical character. It has been shown by 

 van't Hoff that the velocity of chemical reactions is increased 

 twofold or more for each rise of 10 or more in temperature. 

 The temperature co-efficient, therefore, lies between 2 and 3. 

 For most physical processes, on the other hand, the tempera- 

 ture co-efficient lies between 1 and* 2. The temperature 

 co-efficient for the velocity of a nerve impulse is equal to about 2, 

 which indicates that the underlying process is chemical in 

 nature. It is very suggestive that the conductivity of nerve 

 depends upon an adequate supply of oxygen. When a nerve 

 is surrounded by an oxygen-free atmosphere it slowly loses 

 its conductivity, which, however, is promptly restored upon the 

 admission of oxygen. Anesthetics, narcotics, and cold likewise 

 suspend conductivity. 



Just as in muscle functional activity is accompanied, sooner 



