CHAPTER LXIV 

 " ANIMAL ELECTRICITY " 



VARIOUS tissues of the body display electrical currents when in 

 action or when injured. Such currents are sometimes referred to as 

 " animal electricity." If a nerve-muscle preparation be placed upon 

 a glass plate, and by means of a glass rod the 

 free end of the nerve be allowed to touch the 

 muscle, a contraction occurs (Fig. 296). This 

 is an experiment contrived by Galvani to prove 

 the existence of animal electricity. In his first 

 experiment, Galvani used metals. He found that 

 if the hind-limbs with the skin removed be sus- 

 pended from an iron stand by a copper hook 

 passed through the lower part of the vertebral 

 column, contraction of a leg occurs every time it 

 is made to touch the iron stand. He supposed 

 that this contraction was due 'to animal elec- 

 tricity. Volta insisted that it was due to the 

 completion of the circuit between the two metals 

 by the wet tissue of the frog. From the contro- 

 versy between Galvani and Volta came about 

 the invention of the galvanic battery, and the 

 development of electrical science. The discovery 

 of the electric fishes gave the crowning proof of 

 animal electricity. Tho Malapterurus was known 

 to the ancient Egyptians, and figured in their 

 monuments. The electric eel of South America gives a most powerful' 

 shock. The natives used to exhaust wild-horses by driving them 

 into a marsh infested with these eels, and so capture them. 



Animal currents now play an important part in the studj 7 of 

 abnormal conditions of the heart. It was at first believed that natural 

 currents pre-exist in. normal resting tissues, but it is now known that 

 these currents only occur when the chemico-physiological condition 

 of the tissue is altered by activity or injury. 



The Electromotive Properties of Muscle and Nerve. If a normal 

 muscle or nerve be connected by a pair of non-polarizable electrodes 

 to a galvanometer, no deflection of this instrument takes place, show- 

 ing that normal muscle or nerve is isoelectric. Perfectly " normal " 

 muscle is difficult to obtain, since it is necessarily injured in the pre- 

 559 



FIG. 296. DIAGRAM 

 OF GALVAXI'S EX- 

 PERIMENT. CON- 

 TRACTION WITHOUT 

 METALS. 



