THE PRINCIPLES OF EMBRYOLOGY 467 



viz. that the lesion disturbed the chemico-physical equilibrium of an 

 anatomically continuous (neuro-muscular or neuro-epithelial) chain 

 of cells, by separating the non-nervous from the nervous, and that 

 the changes occurring in denervated muscle, which I shall describe 

 later (and possibly those in denervated skin), are in part due to the 

 reciprocal chemico-physical disturbance effected in these tissues by 

 their separation from the nervous tissues ; also that the section of 

 the posterior roots checked the development of those portions of 

 them still attached to the spinal ganglia, because the chemico- 

 physical equilibrium in those processes is maintained not only by 

 the spinal ganglion-cells, but also by the intra-spinal cells with which 

 these processes are anatomically continuous." 



What is seen so strikingly in the new-born animal can be seen 

 also in the adult, and in Anderson's paper references are given 

 to the papers of Lugaro and others which lead to the same 

 conclusion. 



These experiments seem to me distinctly to prove that the 

 connection between the elements of the peripheral organ and the 

 proximate neurone is more than one of contact. 



We can, however, go further than this, for, apart from the 

 observations of Apathy, there is direct physiological evidence that 

 the vitality of other neurones besides the terminal neurunes is 

 dependent upon their connection with the peripheral organ, even 

 though their only connection with the periphery is by way of the 

 terminal neurone. Thus, as is seen from Anderson's experiments, 

 section of the cervical sympathetic nerve in a very young animal 

 causes atrophy of many of the cells in the corresponding intermedio- 

 lateral tract, cells which I supposed gave origin to all the vaso- 

 constrictor, pilomotor, and sweat-gland nerves. A still more striking 

 experiment given by Anderson is the effect of the removal of the 

 periphery upon the inedullation of those efferent fibres which arise 

 from these same spinal cells, for, as he has shown, section of the 

 nerves from the superior cervical ganglion to the periphery in a very 

 young animal delays the medullation in the fibres of the cervical 

 sympathetic — that is, in preganglionic fibres which are not directly 

 connected with the periphery but with the terminal neurones in the 

 superior cervical ganglion. So also on the afferent side a sufficiently 

 extensive removal of sensory field will cause atrophy of the cells of 

 Clarke's column, so that, just as in the case of the primary neurones, 



