THE INJURY CURRENT OF NERVE 
217 
which an explanation might be sought, namely (i) a difference between the chemical 
constitution and physical characteristics of the molecules forming the longitudinal 
surface and transverse section respectively, due to secondary changes (acidity, etc.) at 
the transverse section ;' and (2) a pre-existing difference beween the nerve substance 
proper and its sheath. 2 
The first of these two rejected alternatives is closely akin to Hermann's 
' alteration ' theory, and was dismissed because of the apparent disproportion in extent 
between the phenomenon to be explained and the chemical change which could other- 
wise be demonstrated. The second alternative is as closely akin to Grunhagen's 
theory, and was dismissed because of an apparently decisive contradictory experiment 
(see later). 
Having once selected a line of explanation, his further developments of it were 
foreordained by the scientific attitude of the time, which translated wholesale the 
attributes discoverable within and at the surface of a mass of homogeneous material 
to each of the individual molecules of which it was formed. The peripolar 5 molecule 
was a minute zinc-copper model unit, and its conception was then the necessary out- 
come of the legitimately formed belief that the nerve or muscle fibre was alone the 
physical structure upon which the phenomenon depended, and that this could practically 
be treated as a homogeneous structure. 
Similarly when Du Bois Reymond discovered that under certain circumstances 
the muscle fibre could not be treated as homogeneous, and that the condition then 
present in localized portions of the fibre prevented the demonstration of the phenomenon, 
it was only possible to consider that such localized portions (parelectronomic layer) 4 
offered an opposing eleotromotive force : it not being known that neutral ' mem- 
branes ' might eliminate the display of electrical differences by offering an impermeable 
obstacle to the movement of diffusing particles, and that there was, therefore, no 
necessity to credit such obstacles as were discovered with what one might call 
' electromotive functions.' 
Note on the Parelectronomic Layer 
Du Bois Reymond's conception of the parelectronomic layer has been misunderstood, and even 
ridiculed, as if invented when the trend of a controversy compelled him to meet new evidence and satisfy 
impossible claims upon his original 'peripolar molecule' conception. It may therefore be of some 
advantage to consider the following quotation taken from a book published in 1852, and, therefore, fifteen 
years before the appearance of the 'alteration theory' : — 
H. Bence Jones, Animal Electricity (being an abstract of the discoveries of Emil Du Bois Reymond), 
page 116; published by Churchill, London, 1852 — 'The current obtained from the longitudinal section 
and the natural transverse section is seldom, if ever, so strong as the current obtained from the longitudinal 
1. Monatsberichte A. Konigl. slkad., 2 Berlin, 1859, p. 288. Republished in Du Bois Reymond's Gesammt Abhandl, II, I, 5. 
'After my discovery in 1842 of the muscle current, naturally one of my first experiments was undertaken to discover 
whether the longitudinal surface and the artificial cross section of muscle possessed different reactions.' 
2. Untersuchungen, I, 558. 1848. 
3. Du Bois Reymond, Untersuchungen, I, p. 561, 1848 ; see also C. Morgan, Electrophysiology, etc., p. 279, 1867. 
4. Du Bois Reymond, Untersuchungen, II, p. 39 ; or C. Morgan, loc. cit., pp. 294-309. 
