72 F. O. SCHMITT VOL. 4 (195O) 



polarization experiments^*. The ascendency of the membrane theory together with a 

 growing distrust of structures which can be demonstrated only after fixation caused 

 physiologists to lose interest in morphology as an immediate aid in studying the mecha- 

 nism of impulse propagation. To many physiologists the nerve fibre became essentially 

 a tube limited by a metastable interfacial film and containing a salt solution plus 

 certain metabolizing substances capable, in some way, of maintaining the structural 

 integrity of the fibre and of furnishing the energy needed for impulse propagation. 



The conservative nature of the processes involved in the generation and propa- 

 gation of the spike wave was demonstrated by studies of the thermal and oxidative 

 changes. The excess oxygen consumption per impulse may be very small at low rates 

 of stimulation^^ and, after treatment with azide, nerve is capable of conducting action 

 waves of undiminished amplitude with no accompanying increase in oxygen consump- 

 tion's. 



Currently there is renewed interest in the coupling of reactions of chemical metabo- 

 lism with bioelectric processes. In addition to the much debated question of the role of 

 acetylcholine^^"^^ and of other "Erregungsstoffe"^", suggestions have been offered linking 

 particular chemical reactions with the polarization potentiaP^. ATP-ase has also been 

 invoked^-"^*. However, there is as yet no general agreement as to the role of such sub- 

 stances. 



In the field of electrophysiology much progress has been made in the more accurate 

 description of the electrical properties of the nerve fibre at rest and during activity. 

 However, the present period is characterized by fundamental disagreement among the 

 most competent investigators about the nature, origin and significance of the polari- 

 zation and action potentials^^^^^ Characteristic also is the failure of the electrical studies 

 to provide definitive clues as to the structure and chemical composition of the reacting 

 system. 



The appalling ignorance about the chemical composition, particularly of the 

 proteins, of peripheral nerve may in part be due to the unattractiveness of investigating 

 a tissue in which the structure of interest is presumably a paucimolecular layer of 

 uncertain location. Amino acid analyses have been made on the socalled "neurokeratin" 

 but the location of this protein is uncertain. Originally the term was applied to the pro- 

 tein of the myelin sheath. However, Block^ concluded that it is more probably/ located 

 in the axis cylinder and may be the protein of which the neurofibrils are composed. 

 A pseudo-nucleoprotein was isolated from the axons of the giant fibres of the squid and 

 from lobster nerves^^. Since this complex seems to occur in the central nervous system 

 as well as in peripheral nerve it was considered characteristic of nerve and was termed 

 "neuronin". Its possible relation to neurofibrils is not known. The chemical characteri- 

 zation of this entity is at best very sketchy, but it can at least be definitely localized 

 in the axon. Chemical investigations are now being carried on by J. Folch and his 

 collaborators on the proteins and lipids of the brain. Already a liponucleoprotein and 

 several other proteins have been isolated and partially characterized'*". Though it is 

 impossible at present to say whether these proteins are located in the perikarion, the 

 axon or in extrafibrillar material, it may be possible, once the pure constituents are 

 thoroughly characterized, to devise methods by which their presence in the components 

 of peripheral nerve may be demonstrated. 



In view of the situation as outlined above, it is perhaps not surprising that mor- 

 phological studies have thus far contributed relatively little to an understanding of 

 References p. 76lyy. 



