STRUCTURE OF THE GREY SUBSTANCE OF THE SPINAL CORD. 347 



homogeneous nuclei that again enclose a nucleolus with one or 

 two vacuolse. In many instances the cells contain pigment 

 masses consisting of a variable number of granules, which may 

 not unfrequently be found in the several processes. The form 

 and size of these cells vary to an extraordinary extent, every 

 magnitude from 0*120 of a millimeter downwards being met 

 with. The largest cells occur in the anterior, the smallest in 

 the posterior cornua, and those of middle size in the columns 

 of cells which are confined to the thoracic region of the spinal 

 cord, are situated laterally and behind the central canal, and are 

 known under the name of Clarke's columns. Whilst we possess 

 in the solution of carmine and ammonia, and in chloride of 

 potassium and gold, two excellent reagents for distinguishing 

 the delicate fibrous tissue of the neuroglia from true nerve 

 fibres, we possess no means of establishing a sharp diagnosis 

 between nerve cells and the cellular elements of connective 

 tissue, since both are alike coloured by carmine and ammonia, 

 whilst the chloride of potassium and gold exerts no action 

 upon either. There can, indeed, be no difficulty in distinguish- 

 ing between these and the larger and medium-sized nerve cells, 

 but it is not always easy for even a practised observer to dis- 

 tinguish between the smallest nerve cells and certain cellular 

 elements of connective tissue. 



Two important steps have recently been made in the mor- 

 phology of the nerve cells of the spinal cord. One of these is 

 the discovery by Deiters* of the diversity in the nature of the 

 processes of these cells, and the other is the observation made 

 by M. Schultzef of the fibrillated character of the cell body 

 and the cell processes. In regard to the latter point, I must 

 refer to p. 176, et seq., of the first volume of this work ; the 

 discovery of Deiters, on the other hand, demands a closer 

 examination, since it is of the greatest importance in reference 

 to the mode of origin of the spinal nerves. 



Deiters, in the first place, observed the remarkable fact that, 

 amongst the numerous processes given off from a nerve cell, 



* Loc. tit. , p. 53, et seq. 



t Observations de structura ceUularum fibrarumque nervearum. Bonn, 

 1868. 



