574 



THE NERVOUS SYSTEM 



dividual neurones,* each of which is a more or less complete morphological 

 unit capable of Carrying on certain functions of its own. Each of these 

 neurones maintains physiological continuity with its associates, presumably 



lisi 



B 



^FiG. 358. Spinal Ganglion Cells from the Cat. A, Normal taken before stim- 

 ulation; B, taken after five hours' stimulation. From the right and left, eight thoracic 

 ganglia. (Hodge.) 



by protoplasmic contact rather than by continuity; so that well-marked paths 

 of conduction are possible throughout the extent of the particular mass of 



* "According to the estimations of Meynert, the cortex of the cerebral hemisphere 

 alone contains twelve hundred millions of ganglion cells. Donaldson (The Growth of the 

 Brain, a Study of the Nervous System in Relation to Education, i2mo, London, 1897, 

 P- J 59) states that for the total number of nerve cells in the central nervous system three 

 thousand millions is a moderate estimate." (Barker, the Nervous System and its Con- 

 stituent Neurones, p. 42, 1899.) 



