TROPHIC CENTRES AND NERVES 6l/ 



undoubtedly exist throughout the body, in the sympathetic and in the 

 motor and mixed nerves ; and it is possible that there are vasomotor 

 inhibitory centres, although such centres have not been located. The 

 mode of action of these nerves is analogous to that of the inhibitory 

 nerve of the heart, restraining and regulating the action of vasomotor 

 nerves and allowing the pressure of blood to dilate the vessels. It does 

 not, however, seem proper to call them " vaso-dilator " nerves, any more 

 than it would be correct to call the inhibitory nerve of the heart the 

 cardiac dilator nerve. 



Trophic Centres and Nerves. Collections of nerve-cells act as cen- 

 tres, presiding over the nutrition of the nerve-fibres with which they are 

 connected ; but it has been found that the nutrition of other parts may 

 be profoundly affected through the nervous system. Many patholo- 

 gists, relying on the presence of lesions of cells in the cord, in con- 

 nection with cases of progressive muscular atrophy, admit the existence 

 of trophic cells and nerves. These views, however, rest almost entirely 

 on pathological observations. Experiments on the sympathetic do 

 not positively show any influence on nutrition, except as this system 

 of nerves affects the supply of blood to the parts. When a sympa- 

 thetic nerve is divided, there is an exaggeration of the nutritive processes 

 in particular parts, and there may be inflammatory phenomena, but 

 atrophy of muscles is not observed. Atrophy of muscles, indeed, fol- 

 lows division of cerebro-spinal nerves only, or, as cases of disease have 

 shown, disorganization of cells belonging to what are recognized as 

 motor centres. As regards this condition, there can be no doubt of the 

 fact that progressive muscular atrophy is attended with disorganization 

 of certain of the motor cells of the spinal cord. 



Without fully discussing this subject which properly belongs to 

 pathology the facts may be briefly stated as follows: There may be 

 progressive atrophy of certain muscles, uncomplicated with paralysis 

 except in so far as there is weakness of these muscles due to partial and 

 progressive destruction of their contractile elements. The only constant 

 pathological condition in these cases, aside from the changes in the 

 muscular tissue, is destruction of certain cells in the antero-lateral por- 

 tions of the cord, with more or less atrophy of the corresponding 

 anterior roots of the nerves. It has not been assumed that there are 

 cells in the cord, presenting anatomical peculiarities by which they may 

 be distinguished from the ordinary motor or sensory elements ; but the 

 fact of the degeneration of certain cells (a pigmentary and sclerotic 

 atrophy), others remaining normal, has led to the distinction by writers, 

 of trophic cells, and of course these must be connected with the parts 

 by trophic nerves. 



