THE PRODUCTION OF ENERGY IN MUSCLE 99 



tail to the head. Peculiarly enough, the fish itself is fully protected against these 

 shocks, a fact which is generally referred to the extremely low degree of irritability 

 of its tissues. 



Animal electricity, or as it is known in Physics, galvanism was dis- 

 covered by Alvisio Galvani in 1786. In the course of his experiments 

 upon the influence of atmospheric electrical discharges upon animal 

 life, he attached the leg of a frog to a copper hook and placed this 

 preparation upon the iron railing of the veranda of his house. When 

 he did so, the muscles twitched violently. He explained this phenome- 

 non by saying that the muscles themselves generate electricity. Volta, 

 however, gave a very different and, as it finally proved, more correct 

 explanation of this reaction. He assumed that whenever two dis- 

 similar metals are connected with a moist conductor, a difference in 

 electrical potential is established which is equalized as soon as these 

 metals are joined. Peculiarly enough, Galvani not only adhered to 

 his former contention, but endeavored to find further substantiation 

 for it. He placed a muscle preparation upon a glass plate and brought 

 the end of a freshly cut nerve in contact with its surface. Whenever 

 contact was made between them, the muscle twitched violently. He 

 thus became the discoverer of animal electricity after having just 

 convincingly recognized contact electricity. 



Methods of Detecting Electrical Variations in Muscle. The 

 existence of electrical currents in the tissues of animals and plants 

 did not find direct proof until the year 1824, when Schweigger dis- 

 covered the multiplicator and Nobili the galvanometer. A few years 

 later, Nobili also proved that "natural currents" occur in the frog, 

 which pass in a direction from the foot toward the head of the animal. 



The ordinary form of galvanometer consists of a ring magnet which is suspended 

 by means of a silk fiber and rests in relation with a number of vertical coils, each 

 of which is composed of many windings of fine copper wire. If an electric 

 current is passed through this system of wires, the neighboring magnetic field is 

 influenced in such a way that the magnet is deviated from the magnetic meridian 

 either to the left or right in accordance with the direction of this current. These 

 deviations are registered as a rule by equipping the pointer or needle of the magnet 

 with a small mirror, from the surf ace of which a beam of light may be reflected upon 

 a screen or upon sensitive paper contained in a photographic camera (Thompson). 

 In order to protect the galvanometer against the magnetism of the earth, two 

 magnets of nearly the same strength are placed in opposite directions near the 

 instrument. As the magnets tend to point toward the poles, they oppose one 

 another and thus compensate in part for the earth's magnetism. The Deprez 

 d' Arson val galvanometer embraces certain modifications which, in addition to those 

 just mentioned, diminish the disturbances otherwise prone to result from currents 

 made to traverse neighboring circuits for purposes of light and electric power. The 

 principal element of this instrument is a wire which is hung between the poles of an 

 electromagnet. Inasmuch as this wire is bent upon itself to form a spiral, it is 

 not deflected laterally but is merely twisted in a rotatory manner. Its movements 

 are registered by a mirror from which light is reflected. 



An instrument of similar construction but capable of a much greater rapidity 

 of motion, is the string galvanometer, devised by Einthoven. 1 It consists of a power- 



1 Arch, intern, de Physiol., iv, 1906, 133, and Pfltiger's Archiv, Ixxii, 1908, 517. 



