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THOMPSON YATES LABORATORIES REPORT 
There have first to be considered such factors as polarization, self-induction, and, not 
least, the fact that chemical substances in solution only give rise secondarily, by pro- 
cesses of diffusion, to electrical phenomena. It is not, therefore, surprising- that 
Hermann, in 1898, is somewhat less confident of the truth of the alteration theory 
than in 1867. Its establishment as the prevalent hypothesis has rested not so much 
upon evidence adduced directly to support it as upon evidence which temporarily cut 
the ground from beneath the feet of its opponents. 
It is necessary to realize this fact, and to remember the powers of adverse 
criticism which indefatigable research and a skilful handling of physical and mathe- 
matical detail, and the position of authority which the victory in this controversy and 
the esteem in which his other contributions to physiological literature are held, have 
conferred upon Hermann. 
Section III. Grunhagen 
Grunhagen' in 1866, a year before Hermann's promulgation of the alteration 
theory, advanced a theory, like Du Bois Reymond's in so far that the conditions of 
importance were assumed to be ' pre-existent ' in the nerve before the injury, but 
unlike it in that it involved, as prime factors, conditions existent in the ensheathing 
tissues of the nerve trunk, as well as in the physiologically important elements of 
structure. Grunhagen's advance to this position was due to a consideration of the 
histological structure of the nerve, and to experiments undertaken by him in which 
he brought to notice circumstances of importance hitherto unconsidered in this 
problem : for he discovered in combinations of various solutions and ' membranes ' 
a possible source of definitely-directed electrical currents. 
The first ' membranes ' used by him were porous clay pots, and his explanation 
of the value of the whole combination was given in terms of the capillary pores of - 
these structures, and of the Quincke 2 'diaphragm currents' arising from the passage 
of water through them. Further examination revealed other possible explanations, 
and in 1874 3 one finds him as the discoverer of a ' new kind of electrical current ' as 
distinguished from currents thus originated by the passage of water. This new 
source of electromotive force was, undoubtedly, what would now be described as a 
partially permeable ' membrane ' separating solutions of electrolytes. Of the efficacy 
of such combinations there now seems little room for doubt, as also of the similar 
ones examined previously by Buff in 1854, and ridiculed by Hermann in 1871 
(see later). There can also be little doubt but that Grunhagen insisted upon the 
importance of the membrane in the combinations described by him, and this point 
must be remembered in considering Hermann's criticism. Hermann, one must 
1. Grunhagen, Konigsberger Med. Jalirb. IV, p. 199. 1886. 
2. Quincke, Fogg. Ann. CVII, p. 37, CX, p. 56 ; also paper by Kunkel, Pfiuger's Archiv., XXV, p. 34.2. 1883. 
3. Grunhagen, PJiugera Archiv,, VIII, p. 573. 1874. 
