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362 that medicine is the proper road to that goal. A medical student, then, Du Bois-Reymond became, and as such, a pupil, and soon after an assistant of the great anatomist and physiologist, John Müller.

The connection with Müller decided, as it were, his fate. Humboldt at that time received a copy of Matteucci's "Essai sur les Phénomènes electriques des Animaux," and communicated it to Müller. Müller, knowing that Du Bois-Reymond possessed a share of physical and mathematical knowledge very unusual in a student of physiology, thought him qualified to take in hand the investigation of animal electricity, in which Matteucci had made but a poor advance since Nobili's discovery of the so-called current of the frog. Thus it happened that, in the spring of 1841, Du Bois-Reymond undertook to elucidate the problem proposed to science by Nobili, and for nearly forty years he has not ceased to work upon this subject, which, in his hands, and those of his numerous pupils, has marvelously expanded, so as to become one of the most important branches of physiology.

Du Bois-Reymond, after having in 1842 printed a short account of his first results, went on working patiently for seven years, and then published his celebrated book, "Researches in Animal Electricity" (Berlin, 2 vols., 1848-'49). This work, besides a complete history of what had previously been done upon the subject, contains an immense number of experiments, made after methods, and with the aid of apparatus, for the most part entirely new, invented by Du Bois-Reymond himself. In substance, the book is devoted to the exposition of his discoveries of the muscular and of the nervous current, of their law, and of the variations they undergo when the muscles and nerves are thrown into action.

To understand the importance of these discoveries, it must be borne in mind that, long before Du Bois-Reymond, in fact since the middle of last century, innumerable attempts had been made to observe electrical phenomena during the contraction of the muscle. They had all failed. Du Bois-Reymond, at the outset, perceived that one of the reasons of these failures was the transient nature of the contraction, and he invented the method of tetanizing the muscles in order to increase the duration of the contraction, and thereby facilitate the observation of what takes place in that state. He was thus fortunate enough to detect electrical phenomena concomitant with the act of contraction, and he even taught how to deflect the magnetic needle of the galvanometer by the voluntary contraction of the muscles in living man, or, as it were, by our will. The correctness of these facts having been doubted by MM. Despretz and Becquerel, of the Académie des Sciences, Du Bois-Reymond, in 1850, went to Paris with his apparatus, and triumphantly proved the truth of his statements.

As to the nerve, up to the date of Du Bois-Reymond's researches, no material change had ever been observed during its activity. In this case, too, a great many fruitless attempts had been made to discover