CHAPTER XV 

 ELECTRO-PHYSIOLOGY 



A LITTLE more than a hundred years ago the foundation both of electro- 

 physiology and of the vast science of voltaic electricity was laid by a 

 chance observation of a professor of anatomy in an Italian garden. It 

 js indeed true that long before this electrical fishes were not only 

 popularly known, but the shock of the torpedo had been to a certain 

 extent scientifically studied. But it was with the discovery of Galvani 

 of Bologna that the epoch of fruitful work in electro-physiology began. 

 Engaged in experiments on the effect of static and atmospheric elec- 

 tricity in stimulating animal tissues, he happened one day to notice 

 that some frogs' legs, suspended by copper hooks on an iron railing, 

 twitched whenever the wind brought them into contact with one of 

 the bars (p. 814). He concluded that electrical charges were developed 

 in the animal tissues themselves, and discharged when the circuit was 

 completed. Volta, professor of physics at Pavia, fixing his attention on 

 the fact that in Galvani's experiment the metallic part of the circuit 

 was composed of two metals, maintained that the contact of these was 

 the real origin of the current, and that the tissues served merely as 

 moist conductors to complete the circuit ; and after a controversy lasting 

 for more than a decade, he finally clinched his argument by constructing 

 the voltaic pile, a series of copper and zinc discs, every two pairs of 

 which were separated by a disc of wet cloth, or paper moistened with salt 

 solution. The pile yielded a continuous current of electricity. 'So,' 

 said Volta, ' it is clear that the tissue in Galvani's experiment only acts 

 the part of the cloth.' Galvani, however, had shown in the meantime 

 that contraction without metals could be obtained by dropping the nerve 

 of a preparation on to the muscle (p. 814) ; and it soon began to be recog- 

 nized that both Galvani and Volta were in part right, that the tissues 

 produce electricity, and that the contact of different metals does so 

 too. Although it is curious to note how completely the growth of 

 that science of which Volta's discovery was the germ has overshadowed 

 the parent tree planted by the hand of Galvani, yet animal electricity 

 has been deeply studied by a large number of observers, and many 

 interesting and important facts have been brought to light. 



Since it is in muscle and nerve that the phenomena of electro- 

 physiology are seen in their simplest expression, and have been 

 chiefly studied, we shall develop the fundamental laws with reference 

 to muscle and nerve alone, and afterwards apply them to other 

 excitable tissues. 



i. All points of an uninjured resting muscle or nerve are approxi- 

 mately at the same potential (or iso- electric}. In other words, if any 



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