354 THE SPINAL CORD, BY J. GERLACH. 



to the question, as I have made a special examination of a par- 

 ticular group of cells of medium size situated near the centre of 

 the medulla, and therefore about equidistant from the point of 

 entrance of both the anterior and posterior roots into the grey 

 substance. This group is the already-mentioned cell layer 

 limited on each side to the cervical portion of the spinal cord, 

 and together known as Clarke's columns. As these are not 

 readily discoverable in the fresh spinal cord, I selected speci- 

 mens that had been slightly hardened in bichromate of am- 

 monia, but only so far as to enable transverse sections to be 

 made. These sections were tinted with carmine and ammonia, 

 and then placed in glycerine, in which they soon acquired a 

 degree of hardness fitting them to be teazed out with needles. 

 In sections of the cord thus prepared I was able with facility, 

 under a low power, to isolate for considerable distances the 

 nerve- process of the large cells of the anterior horns, and also 

 of the smaller cells from the middle portion of the grey sub- 

 stance. In the nerve cells of Clarke's columns, on the contrary, 

 I was unable in any one instance to discover a nerve-process. 

 As I now possess considerable experience in this kind of inves- 

 tigation, and could not easily overlook the nerve-process, even 

 if it were abruptly broken off, I believe I may say with tolera- 

 ble confidence, that all ganglion cells do not possess a nerve- 

 process. We must therefore admit the existence in the spinal 

 cord of two morphologically different kinds of nerve cells, of 

 which the one is in direct connection with the fibres of the 

 anterior roots and the nerve-fibre plexus of the grey sub- 

 stance, whilst the other only communicates with the latter. 



The idea immediately suggests itself, that these, in an ana- 

 tomical point of view, sharply differentiated cells of the spinal 

 cord possess a different physiological significance, though I do 

 not overlook that it is always a difficult and very dubious 

 proceeding to draw physiological conclusions from purely 

 morphological considerations. Moreover the researches made 

 upon the spinal cord in regard to this point are insufficient for 

 comparison. Jacubowitsch,* it is well known, transferred the 



* Mittheilungen iiber den feineren Ban von Gehirn und Mark. "Obser- 

 vations on the finer Structure of the Brain and Spinal Cord." Breslau, 

 1857. 



