Manchester Memoirs, Vol. xlii. (iZ^Z), No.\%. 43 



This, at first sight, seems inconsistent with the broad 

 experience that the work of the nervous system, above 

 that of all other parts of the body, becomes richer and 

 fuller as life advances. But it is only inconsistent with 

 the view that in the course of life there come to the indi- 

 vidual new powers, the outcome of new units of machinery. 

 It is not inconsistent with the view that new powers are 

 only the development of the potentialities of old units. 

 And, indeed, the failure to produce new units brings as a 

 recompense favourable conditions for the development of 

 such potentialities. In the nerve unit, the nerve cell, the, 

 to us, occult energies — which in another tissue lead to the 

 cell sacrificing itself in order to produce its kind — are 

 selfishly limited to the increase of its own mass and powers. 

 Barred from reproduction, the nerve-cell is conspicuous, 

 on the one hand, for its power to extend parts of its body 

 for enormous distances from its central nucleus, and to 

 repair any parts of itself which may be damaged or injured; 

 and, on the other hand, for the facility with which it adapts 

 its growth to the circumstances of its life. 



Thus, the axon of a cell in the lumbar cord, or the 

 fibre, call it axon or dendrite, belonging to a cell in the 

 ganglion of the root of a lumbar nerve, may stretch away 

 from the nucleus by which its life is governed right down 

 to the toes, and, moreover, if divided close to the nucleus 

 so that the whole length dies away, will in a very short 

 time be renewed from the nucleus outwards to its very 

 end. Take away the nucleus and perikaryon, no new 

 nucleus, no new cell ever replaces the lost; but leave 

 the nucleus, and a great long axon, many times exceeding 

 the perikaryon in bulk, may be renewed again and again. 



So, again, while, as I have said, we have no evidence 

 that after a certain date any new nerve cell ever makes 

 its appearance, we have abundant evidence that a nerve 

 cell, simple in form at its installation in early life, may 



