328 THE ANIMAL AS A PRIME MOVER. 



that electricity is produced in the muscular and nervous systems, 

 in vertebrate animals, and that in some cases, as in that of the electric 

 eel, in large quantities, and for peculiar and special purposes of offense 

 and defense. The firefly also produces light for its own special pur- 

 poses. It is supposed by some authorities that electricity is developed 

 for the use of the internal telegraphic system of all animals and it is a 

 " singular" product only in the sense that we have not yet been able to 

 make ourselves familiar with it and to determine just how it is employed 

 and in what manner it is generated and transformed. In the case of 

 the light producer, the product is "singular" in the sense that it is not 

 only unfamiliar as a system of energy production, distribution, and 

 transformation, but also as being rarely developed. We know only the 

 glowworm, the firefly, and a few other organisms, such as the animal- 

 culse of the tropical seas and certain bacteria, which are capable of 

 transforming energy supplied them into light. In this case it is also 

 singular that the light produced should be almost, if not entirely, 

 unmixed with heat, and in this sense it is the most economical light 

 production known. These two examples of singular product are so 

 important and suggestive, as well as interesting from their mystery, 

 that they demand careful consideration, particularly at the hands of the 

 engineer. 



Electricity has long been recognized as a vital energy, and the fame 

 of Galvani, the distinguished professor of comparative anatomy at 

 Bologna (1737-1798) was mainly established by his striking discovery 

 (1786) of what is now familiar to biologist and physicist alike, as 

 " animal electricity," or, as Daguin calls it, 1 'electricity vitale, the " vital 

 fluid," according to the discoverer himself. The famous controversy 

 which at once arose between Galvani and Yolta, the contemporary 

 professor of physics at Pavia, and which led to the publication of Volta's 

 dictum : " When two heterogeneous substances are in juxtaposition, 

 the one always assumes the positive the other the negative electrical 

 state," was a first step toward the determination of the fact that as 

 externally produced currents will always affect the nerves and muscles, 

 so internal currents may always be found capable of affecting external 

 substances. Nobili's discovery of tbe " proper current" directed from 

 the foot toward the head of the frog (1827), as predicted by Humboldt 

 just thirty years earlier; Matteucci's extended researches of later date, 

 and the still more striking investigations of Bu Bois Reyinond (1842), 

 have proven both the existence of such currents in the animal machine 

 and a drift, also, of electricity outward from interior of muscle, or nerve, 

 to the surface, which may probably be taken as a " leakage current," 

 due, in part at least, to tbe fact that, even here, insulation is not perfect. 

 The last-named investigator showed that the more powerful tbe muscle, 

 in its natural condition, the stronger these electric currents, the heart, 

 for example, exhibiting powerful currents and tbe muscular system of 

 the intestines a comparatively weak flow. His well-known experiment, 



