188 SCIENCE PROGRESS. 



shape in the diagram and table that I now submit to 

 criticism, and which has served me as a lecture text for the 

 last two years to my more advanced students. I may 

 emphasise here, as I have done viva voce, that the diagram 

 embodies a mere speculation, but a speculation that, even 

 if false, binds together under one generalising bracket three 

 dicta, two of which are now universally admitted to signify 

 correct data, while the third, although more recent, is also 

 allowed to rank amono; admitted data. These are : — 



(i) A nerve-cell has a trophic influence upon a nerve- 

 fibre. 



(2) Nervous impulses pass round the nervous system 

 in one direction only. 



(3) A nerve-cell is in protoplasmic continuity with a 

 nerve-fibre by one pole only. 



The dependence of (r) and (2), which are statements 

 of well-assured physiological fact, upon (3), which is a 

 statement of less well-assured anatomical fact, will be at 

 once brought clearly before the mind by referring to the 

 case in which they most obviously apply, viz., the anterior 

 cornual cells and their relations to pyramidal and motor 

 fibres. These relations can be most easily exhibited in the 

 following diagram : — 



A pyramidal fibre py terminates in a pericellular 

 J:, feltwork of fibrils, and is not in protoplasmic con- 

 tinuity with an anterior cornual cell. 

 ^ A motor fibre 111 is in protoplasmic continuity 



, with an anterior cornual cell. 



After a section at 1, degeneration occurs below 

 the point of section as far as but not beyond the 

 cornual cell ; there is no degeneration above. 



x^fter a section at 2, degeneration occurs below the point 

 of section, and not above. 



Nervous impulses can be transmitted in a downward 

 direction through the cell from py to m, but cannot be 

 transmitted in an upward direction from m to py} 



1 Gotch and Horsley find — or more correctly speaking infer - that the 

 anterior cornual cells block centrifugal impulses partially, and centripetal 

 impulses completely, but strangely enough neglect the best and best- 



