158 AN AMERICAN TEXT-BOOK OF PHYSIOLOGY. 



is largely based on the remarkable results which have been obtained by the 

 study of artificial models of nerves, called core-conductors. These were first 

 carefully studied by Hermann, 1 and since then by Boruttau, 2 Waller, 3 and 

 others. Such a model can be made by placing a platinum wire in a glass 

 tube, and surrounding it with a 0.6 per cent, salt solution. The wire represents 

 the axis-cylinder of the nerve, and the salt solution the medullary sheath. 

 In other models both core and sheath have been made of fluid electrolytes. 

 With such a core-conductor, one can observe electrical phenomena so closely 

 resembling those manifested by the normal nerve that the statement has 

 been made that all the electrical phenomena of the living nerve can be 

 explained if one will look upon it as a core-conductor. 4 According to this 

 idea, conduction in nerve depends on the transmission of an electrical phase 

 caused by local differences in potential, resulting from chemical changes and 

 consequent polarization effects produced when the nerve is excited. 



This extreme view is accepted by few physiologists. 5 The electrical effects 

 which follow excitation are exhibited not only by nerves, but also by a great 

 variety of protoplasmic structures; they are stopped by anaesthetics, which 

 do not alter the core-conductor-like structure of the nerve, and are greatly 

 modified by all influences which are capable of changing the irritability of 

 living protoplasm, even though they are too feeble to produce any recogniz- 

 able change in dead matter ; finally, they are called forth, not only by electric 

 currents, but by every form of stimulus capable of exciting living protoplasm 

 to action. 



It is very easy to be led astray by the similarity of processes observable 

 on very different structures, and think to see the whole truth in what is only 

 a partial truth. As Engelmann has shown, the anisotropic substance in a 

 piece of catgut suspended in water will cause it to shorten and then lengthen 

 if quickly heated and then cooled, and if a lever be connected with it, to 

 write a curve strikingly like that of the contracting muscle. In muscle there 

 is anisotropic material surrounded by fluid, and heat is produced at the 

 instant of contraction; it is doubtful, however, whether the physiological 

 contraction process is of the same type as that of the piece of catgut. Within 

 the body we have oxidation processes going on, and heat is liberated as it is 

 outside of the body in combustion, but the two sets of changes giving this 

 result are not identical. Similarly we may say that the heart is a pump, and 

 the eye a camera, but the behavior of these living organs is very different 

 from that of lifeless machines. 



All physiological phenomena are to be regarded as of chcmico-physical 

 nature, but many of them differ so widely from the chemical and physical 

 processes associated with dead matter that a sharp distinction should be 



1 Pjliiger's Archiv, 1872, Bd. v.. vi., vii.; also Handbuch der Phyriologie, 1879, Bd. ii. S. 17. 



2 Pflug&>s Archiv, L894-1897, Bd. Iviii., lix., lxiii., lxv., lxvi., Ixix. 

 • Lectures on Animal Electricity, London, 1897. 



4 Boruttau: Pfliiger'a Archiv, 1894, lid. Iviii. S. 64. 



5 Biedermann : I^lectrophysioloyy, translated by F. A. VVelby, 1898, vol. ii. p. 303. 



