1 86 ELEMENTARY LESSONS ON [CHAP. HI. 



Art. 148 as leading ultimately to the discovery of the 

 Voltaic Pile) that when nerve and muscle touch two 

 dissimilar metals in contact with one another a con- 

 traction of the muscle takes place. The limbs of the 

 frog, prepared as directed by Galvani, are shown in Fig. 

 94. After the animal has been killed the hind limbs 

 are detached and skinned ; the crural nerves and their 

 attachments to the lumbar vertebrae remaining. For 

 some hours after death the limbs retain their contractile 

 power. The frog's limbs thus prepared form an ex- 

 cessively delicate galvanoscope : with them, for example, 

 the excessively delicate induction-currents of the tele- 

 phone (Lesson XL.) can be shown, though the most 

 sensitive galvanometers barely detect them. Galvani 

 and Aldini proved that other creatures undergo like 

 effects. With a pile of i oo pairs Aldini experimented 

 on newly killed sheep, oxen, and rabbits, and found them 

 to suffer spasmodic muscular contractions. Humboldt 

 proved the same on fishes ; and Zanotti, by sending a 

 current through a newly killed grasshopper, caused it to 

 emit its familiar chirp. Aldini, and later Dr. Ure of 

 Glasgow, experimented on the bodies of executed crimi- 

 nals, with a success terrible to behold. The facial 

 muscles underwent horrible contortions, and the chest 

 heaved with the contraction of the diaphragm. This 

 has suggested the employment of electric currents as an 

 adjunct in reviving persons who have been drowned, the 

 contraction of the muscles of the chest serving to start 

 respiration into activity. The small muscles attached 

 to the roots of the hairs of the head appear to be 

 be markedly sensitive to electrical conditions from the 

 readiness with which electrification causes the hair to 

 stand on end. 



23O. Conditions of Muscular Contraction. To 

 produce muscular contraction the current must traverse 

 a portion of the nerve longitudinally. In a freshly pre- 

 pared frog the current causes a contraction only momen- 



