THE ANIMAL A MACHINE 195 



no metals at all. Instead they do have various kinds of 

 fatty material and proteins. Can those organic materials 

 give rise to electrical charges and currents? 



Science has investigated and discussed this problem for 

 150 years; still the solution is not at hand and may not be 

 for another century or two. Formerly it was even ques- 

 tioned whether living tissue can give rise to electric currents, 

 but at present there can be no doubt about it. 



To form an idea of the magnitude of the electric effects 

 produced by tissue, we may compare them to those of 

 ordinary batteries. The charge of a flashlight battery is 

 measured whenever it is sold in a store; a single cell of such 

 a battery, when it is good and fresh, measures 1.5 volts. 

 The charge of a lead battery as used in automobiles is 2 

 volts for each cell. Since there are usually three cells con- 

 nected in series, the entire battery has a charge of 6 volts. 

 But the charge which travels along a nerve fiber is much 

 smaller, only 0.05 to 0.1 volt. This feeble charge is gen- 

 erated in an unknown manner somewhere in the brain or 

 other tissue. 



There are, however, instances in which animal tissue may 

 give rise to very much larger charges: in certain types of 

 "electric fish" the charge may rise to nearly 100 volts. 

 These creatures have special electric organs which consist 

 of very thin discs, superimposed like stacked-up squares. 

 These discs are made of fat, or a similar material, and are 

 separated by a liquid, or by gelatinized layers of some sort. 

 The whole electric organ thus resembles a Volta cell or a 

 modern "layer-built" battery commonly on sale in radio 

 stores. They consist of alternating layers of metallic plates 

 with gelatinized watery layers between them. The electric 

 organ of a fish is also layer-built, but substitutes layers of 

 fat or some other organic material for metallic plates. Each 

 layer of this organ is extremely small, but all together make 



