TROPHIC FUNCTIONS OF THE SPINA I CORD. 877 



other peripheral tissue, the skeletal muscles are governed by the efferent 

 root cell system of nerve cells. No other tissue, except skeletal muscle, 

 practically dies down, in consequence of injury of the root cell system. 



The inflammation so prone to occur in exposed sensifacient surfaces, 

 when their nerve channels are broken, does not stand in such direct 

 relation to the nerve injury. The anaesthesia and analgesia of the 

 surface lead to the unperceived accumulation of irritant effects. The 

 most exposed part of the apaesthetic limb is the seat of ulceration, as 

 the result of long-continued and undue — because unperceived — pressure. 

 The keratitis often ensuing on section of the trigeminus can be avoided 

 by careful protection of the eye from dirt. The ulceration about the 

 lips after a similar unilateral lesion, has been noted to extend quite 

 freely across the median line, so that there seems no difference be- 

 tween the essential resistance of the anaesthetic and of the normal tissue. 

 The broncho-pneumonia, after vagotomy, seems entirely explicable by 

 irritation of the respiratory tract from particles inhaled or entering from 

 the digestive tract, the former tract being no longer securely guarded 

 from this accidental leakage of material from the latter. 



Not only are the nerve cells in the above cases trophic for peripheral 

 tissues, but some nerve cells are trophic for other nerve cells, some nerve 

 cell systems trophic for other nerve cell systems. It will have been 

 remarked, from the foregoing paragraph, that the direction of the trophic 

 influence is the same as that of the normal nerve conduction, that is, for 

 instance, from motor root cell to muscle fibre, and not from muscle fibre 

 to motor root cell. So in the cell systems of the cord and brain. Section 

 of an optic nerve leads to trophic changes in the cells of the pulvinar, 

 internal geniculate body, anterior corpus quadrigeminum, etc. If the 

 section be made before the growth of the dependent cells is com- 

 plete, their further growth is hindered. Thence results Gudden's or 

 agenesic atrophy. A series of many links of a nerve cell chain may be 

 affected by it, indeed the whole chain from end to end. But the 

 damage must, in order to effect that result, be at the end which is the 

 seat of excitation of its normal function. The sensory root cell is the 

 alpha of each and every neural series, whatever the function and what- 

 ever the complexity, On the afferent root cell is therefore based the 

 trophism of the whole nerve system, so far as there is a nervous system 

 possessing solidarity as a whole, above and beyond the individual entity 

 of the component cells. After severance of the afferent roots, the 

 motor root cells of their spinal region soon present recognisable struc- 

 tural change. 1 The nucleus of the motor root cell becomes markedly 

 excentric in position, the Nissl bodies become very small or disappear, or 

 lose their normal colour reaction ; the cell becomes large, and the nucleus 

 may even disappear. These changes do not occur with all the ventral 

 horn cells, but only with certain of them ; the larger number of cells reveal 

 no distinct alteration, and in the cells of the lateral horn no change is 

 detected. The nutritive condition of the afferent root cells themselves 

 is to some extent governed by the sensifacient organs that regularly 

 play upon their distal extremities. Hence probably the atrophy of the 



1 W. B. AVarrington, Joum. Physiol., Cambridge and London, 1897, vol. xx. A full 

 bibliography is given in Warrington's paper. For further aspects of the question of 

 the relation between the visible structure of the nerve cell and its functional condition, 

 reference must be made to the article " Nerve-Cell," in this volume. 



