498 SCIENCE PROGRESS 



headings of "injury" and " kathodal state," and the circum- 

 stances inferred from this as characteristic of excitation, are 

 of the same order as those observed as a consequence of 

 the excitation of extracellular material — as, for example, in the 

 case of bone matrix, in which the setting of the matrix was 

 attended with a demonstration of calcium salts. 



It is necessary to explain at this stage an omission, which 

 to the expert may seem of much account, namely, the absence 

 of any reference to the finer details of the minute structure of 

 the core. Histologists, whose views of structure are too fre- 

 quently obtained from tissues altered by the precipitating 

 effects of "fixatives," describe in this core long lines of a more 

 refractive material which run parallel one with another and are 

 separated by and surrounded with material of a simpler kind. 

 The critic may say that the considerations which have taken 

 us within the core should have taken us further. The point 

 assumes importance since from several sides these neurofibrils 

 have been accredited with the functions of the fibre. I have 

 myself made theoretical use of such structures, but have been 

 compelled to abandon them in consequence of a prolonged 

 acquaintance with the appearance of nerve-fibres immersed in 

 the fresh state in simple saline solutions. Neurofibrils are not 

 seen under such conditions. This being the case, their admis- 

 sion into the summary of experimental evidence is hardly 

 justified. It will be remembered that in the case of bone- 

 formation fibrils are precipitated in the material as it sets, and 

 that their arrangement is possibly assignable to forces in action 

 at the moment of setting. It is possible that neurofibrils are 

 similarly formed. If so, it is also possible that they are formed 

 at a time when the setting of the colloidal solution of the 

 nerve-fibre has attained a degree not arrived at during normal 

 functional life. 



Here at last, at the end of the evidence, one feels the demand 

 for a constructive policy to guide further experimental work. 

 If biogen molecules and "ion proteids" — the latter representing 

 a concession, it is true— obscure many points of physical interest 

 in the structure and function of nerve-fibres, and if the core- 

 model theory is set on one side whilst a debate is arranged as 

 to the nature and meaning of neurofibrils, what conception can 

 be placed in their stead? Is there any "opening" along which 

 the game can be further played with as much success as along 



