494 SCIENCE PROGRESS 



Immerse a nerve-trunk in water or in dilute solutions, it becomes 

 turgid, and in consequence as rigid as a stick. Immerse it in 

 concentrated solutions, it loses in weight and becomes abnor- 

 mally crenated and limp. Watched under the microscope 

 individual fibres may be seen to undergo corresponding change. 

 Passing in review the materials in solution within the core it is 

 at once obvious that, as in the case of other tissues also, the 

 number of molecules of simple bodies like the inorganic salts 

 is overwhelmingly great in comparison to the number of the 

 huge protein molecules with which the concept " biogen " is 

 inextricably associated. Experiments of this type are of such 

 a nature as to give us some knowledge of the number of mole- 

 cules within the core, a number to which the inorganic salts 

 present contribute a share so great that the contribution of other 

 matter is negligible.^ From such experiments there is promise 

 therefore of obtaining a quantitative value for the inorganic 

 salts, and that is almost equivalent to the value of the electrolytes 

 within the core. Here, then, is a road to the knowledge imme- 

 diately required to fill the gap in the data requisite for a proper 

 discussion of the core-model theory. It is unfortunately the 

 case, however, that this road has been shown not to be a high 

 road. The information obtained is not of such direct value 

 as it seems, since it has been found that a balance is not 

 necessarily obtained by equalising the salt-content of the internal 

 and external solutions. Such knowledge, then, is of value, but 

 is apprised as only one of the items necessary to a complete 

 understanding of the case. 



We expectantly turn, therefore, to another method which 

 promises to provide further information as to this core in so 

 far as it can be treated as a solution of electrolytes. An 

 electrode placed upon the core exposed at a cross-section of 

 a nerve-trunk is electrically negative to a similar electrode 

 placed upon the uninjured longitudinal surface. This fact is 

 with great probability to be assigned to a diff'erence in the 

 solutions present in these two situations, and to the nature of 

 the membrane formed by the sheath of the fibres, which limits 

 the diffusion capable of taking place between the solutions in the 

 interior of the nerve-trunk. 



In the concentration cell so formed one of the solutions 



^ Carbonic acid molecules are not considered in this case, since the surfaces are 

 permeable to them. 



