390 THE PRODUCTION OF HEAT, LIGHT, AND ELECTRICITY 



to an external current l . The processes of diosmosis and of diffusion may,, 

 therefore, give rise to electrical currents, which may indeed be produced in 

 various ways by differences of concentration. All these are factors within 

 the control of the organism, and capable of alteration by appropriate 

 metabolic activity. 



In all cases it depends upon circumstances whether any current 

 perceptible externally is produced. For instance if a zinc-copper couple 

 is completely immersed in dilute sulphuric acid, the whole of the liberated 

 chemical energy is ultimately transformed into heat, no external current 

 being perceptible. In the same way no differences of potential need exist 

 on the surface of a cell when internal electrical currents circulate in the 

 cytoplasm or cell-sap, and these are impossible to demonstrate in small 

 plant-cells. It is, however, possible to demonstrate the existence of 

 differences of electrical potential between the different parts of the inter- 

 nodal cells of Nitella. 



Bernstein - considers that in muscle-tissue the differences of electrical 

 potential are produced by the action of temperature, and not by chemical 

 changes, a rise of temperature increasing the electro-motive force in a chain 

 of rising concentration. In the case of plants, however, other factors may 

 come into play, and most animal physiologists regard the electro-motive 

 force as being directly derived from chemical changes 3 . 



The occasional existence of externally perceptible electrical currents in 

 dead organs is hardly surprising when we consider that the metabolic 

 products may be at first unequally distributed and that by their diffusion and 

 chemical interaction differences of potential may be produced 4 . Naturally 

 also, such currents gradually diminish and disappear, and the disappearance 

 may be so rapid that in the dead organ no currents can be detected. These 

 post-mortem currents may in part represent actions which go on during life, 

 but in all cases the cessation of metabolism immediately influences the 



1 Cf. Ostwald, Zeitschr. f. physik. Chem., 1890, Bd. VI, p. 69; Walden, ibid., 1892, Bd. X r 

 p. 718; Oker-Blom, Pfliiger's Archiv f. Physiol., 1901, Bd. LXXXIV, p. 191. On concentration 

 chains cf. Ostwald, Lehrb. d. allgem. Chemie, I.e., p. 824; Grundriss, 1. c., p. 442. 



3 Bernstein, Pfliiger's Archiv f. Physiologic, 1902, Bd. XCII, p. 521. Here and in Winkelmann's 

 Handbuch d. Physik, 1903, p. 420, full details are given as to the required temperatures. 



8 Biedermann (Elektro physiologic, 1895, p. 300), L. Hermann, and E. Hering (Lotos, 1889, 

 N. F., Bd. IX, p. 56) all ascribe animal electricity to chemical processes. Du Bois-Reymond con- 

 sidered the phenomena to result from the special arrangements of bipolar molecules, but left the 

 sources of energy an open question. 



4 Ranke (Sitzungsb. d. Bayrischen Akad., 1892, p. 181) and Munk (Die elektrischen u. Bewe- 

 gungserscheinungen im Blatte von Dionaea, 1876, p. 43) observed a gradual disappearance of the 

 electrical currents from dead organs. B. Velten (Bot. Ztg., 1876, p. 296) and O. Haake (Flora, 

 1892, p. 467, footnote) found that currents persisted for a time after sudden killing by steam or hot 

 water. Haake states that the current disappears rapidly from a dead stem of Pisum in moist air, 

 but reappears on laying in water, probably because of the differences of concentration produced by 

 the outward diffusion. According to Waller (Centralbl. f. Physiol., 1901, Bd. XV, p. 480) death 

 by cold is accompanied by a sudden ' explosive ' production of electricity. 



