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/4JV T L i \-^r 



/ y^ 4 ^ * ^ THE NERVOUS SYSTEM. 



j- J f (d) CHANGES"IN THE CELL BODY BESULTING FROM LESIONS TO ITS 

 \Aij' -/DENDRITES. In the study of the effect upon the cell body of a lesion 

 ' A^ J depriving it of one or all of its dendritic processes, we meet with the 

 ;,same experimental obstacles already mentioned in connection with changes 

 v \in the dendrites. It is, again, only in the peripheral arm of the spinal 

 ganglion cell that we have a cellulipetal process of any considerable 

 . J length. Section of this process results in changes in the spinal gan- 

 glion cell quite similar in character to the so-called "axoual" degenera- 

 tion (Plate XIII. , 6). If we consider that a cell's dendrites probably 

 furnish its most important avenue for the reception of impulses, it follows 

 \tthat a neurone may be thrown as completely out of circuit, as it were, 

 1 /ly injury to its deudrites as by injury to its axone. The experiments 

 of Warrington ' are interesting in this connection. He attempted to 

 bring about the same functional effect as would result from section of a 

 cell's dendrites, by inhibiting afferent impulses. Cutting the posterior 

 roots, he noted changes in the cells of the anterior horn. The inference 

 was that these changes were induced by an inhibition of the customary 

 normal stimulation by means of the afferent impulses reaching the cells 

 rough their dendritic processes. 



II. Changes in the Neurone from Interference with its Nutrition. Changes 

 apparently of a degenerative character have been described in neurones 

 as a result of interference with nutrition. Thus Brieger and Ehrlich 2 ^- 

 found that by temporarily applying a ligature to the abdominal aorta, 

 they induced an acute necrosis of the cells of the lumbar cord. - 

 Later experiments of a similar nature followed by the Marchi staining 

 showed that the degenerative process affected not only the cell bodies, 

 but the entire neurone. Similar degenerative changes have been induced 

 by experimentally produced multiple emboli, cells in the vicinity of the 

 occluded vessels being in marked contrast to cells from regions whose 

 vessels remained patent. Ewing 3 describes marked degenerative changes 

 in nerve cells as a result of anaemia consecutive to pressure from cere- 

 bral haemorrhage and to thrombosis of the basilar artery. Less marked 

 changes have been observed in cases of general malnutrition and in se- 

 vere anaemias. 



III. Effects of Toxins upon Neurones, Changes of a degenerative char- 

 acter occur in neurones as a result of the action of toxins. These toxins 

 may be introduced into the body from without, for example, such poi- 

 sons as alcohol, arsenic, lead, strychnine, etc. ; they may be elaborated 

 within the body as the result of faulty metabolism, for example, in urae- 

 mia, eclampsia, etc. , or as a result of the action of bacteria, as in tetanus, 

 rabies (Plate XIII., 3, 4, and 8), diphtheria, etc., or of the Plasmodium 

 malarias. The effects of these poisons upon the neurone vary with dif- 



1 Warrington, W. R, "On the Structural Alterations in Nerve Cells." Jour, of 

 Physiol., London, vol. xxiii., 1898. 



2 Brieger und Ehrlich, "Ueber die Ausschaltung des Lendenmarkgrati." Zeitschr. 

 f. klin. Med., Berlin, Bd. vii., Suppl., 1883-84. 



3 Ewing, J., "Studies on Ganglion Cells." Arch, of Neur. and Psychopath., vol. 

 i., 1898. 



