ON THE NEURON 335 



not continuity, being thus secured, and combined, nervine, 

 and intellectual, operations, made possible. 



With the statement, or histological deduction, that the 

 neuron is incapable of renewal, and that, as the systemic 

 nervous system begins, so it must continue, so far as the 

 gross number of its neuronal units is concerned, we find 

 no fault, except that, it seems impossible, if it be absolutely 

 true, to account for the extremes, of motor dexterity 

 acquired, and the intellectual attainments possessed, or 

 achieved, by certain members of the animal kingdom, and 

 many individuals, and groups of the human family. In 

 the face of these occurrences, if the number of the neurons 

 remains the same, we seemed to be compelled to accept, 

 of some such view as the following, viz. that the 

 neuronal bodies remain in numbers unaltered, but that 

 their textural attachments, prolongations, or processes, 

 may undergo a change, both of addition, and subtraction, 

 as when a neuron, or group, of neurons, are kept in 

 sustained activity, or allowed to remain in functional 

 abeyance, respectively. In the former, we think, we are 

 warranted in assuming, that the lateral dendritic processes 

 undergo a process of, strengthening, and acquired dexterity, 

 so to speak, from exercise, while the latter droop, and 

 atrophy, from continued disuse ; this strengthening, and 

 increased dexterity, so to speak, of amoeboid projection, 

 of dendritic processes, begotten of continued, and well- 

 directed, use, would, therefore, appear to meet the 

 requirements of a belief, in the theory of the unalterability 

 of the original gross number of neuronal units. 



From the origin of the first neurons, in the incipient 

 stages of embryonic development, amid the latent potential 

 matrix of the epiblastic area, a process of continued, but 

 strictly limited addition, or accretion, so to speak, of 

 neuronal units, goes on, whereby the completed systemic 

 nervous system is built up, and projected into every recess, 

 and structure, of the meso- and hypo-blastic areas, thereby 

 assisting in, innervating, vitalising, organising, and sustain- 

 ing in life, these latter, and maintaining in one, living, and 

 co-operating, whole, the combined sympathetico-systemic 

 anatomical elements, of which living animal bodies are 

 composed. The primitive streak, in succession to the 



