THE NEURON 



571 



ing the nerve with cobalt sodium hexanitrite, and after washing 

 differentiating as a black precipitate by adding ammonium sulphide. 

 Such methods destroy the integrity of the nerve, and set free the 

 salts from their combination with the colloidal living substance. 



It is claimed that there is laid down in the cytoplasm of the cell 

 for the purposes of conduction a system of neuro-fibrils, which run 



Fro. 310. 



1, Large Betz cell from human cerebral cortex, showing Nissl's granules and cone 

 of origin of axon at the base. 2, Medium-sized pyramidal association cell. 

 3, Anterior cornual cell. 4, Posterior root ganglion cell. (Mott.) 



j f. 



from end to end of the cell processes. According to some authorities, 

 the neurofibrils are not confined to one nerve unit, but freely leave one 

 neuron and pass into another, thus forming a network throughout the 

 whole nervous system. The study of the living nerve cell does not 

 reveal these fibrils; they are artefacts produced by the method of 

 preparation. 



FIG. 311. PORTION OF A MEDTJLLATED XERVE-FIBRE FROM A. M/.MMAL. 



Another type of neuron is the bipolar nerve cell (Fig. 309). In 

 mammals, these occur only in the ganglia in connection with the 

 eighth nerve; in fishes, they are found in the spinal ganglia, also. The 

 cell body is elliptical in shape, with two processes given off from the 

 two ends of the ellipse. Such a cell is the parent cell of the unipolar 



