WALLERIAN DEGENERATION 575 



which the neurone is a part, and throughout the adjacent masses. By this 

 view, paths of conduction are made up of series or chains of individual neu- 

 rones which are in physiological continuity. 



The Characteristics of the Individual Neurone. The function of 

 the nerve cell may be discussed under two headings: The function of the 

 cell body, and the function of the cell processes. 



The cell body of the neurone is the part that contains the nucleus and is 

 the center of those activities which influence the metabolism of the cell itself. 

 If the cell body be isolated from its processes, the processes will degenerate, 

 while the body continues to live. In other words, the cell body may be con- 

 sidered as the center of those trophic influences which regulate the nutrition 

 of the processes. Although the nerve cell as a whole is in many, perhaps in 

 most, cases a conducting organ, still those physiological processes which go on 

 in it produce marked changes in the protoplasm of the cell body. Hodge 

 has demonstrated that nerve cells which have been active for several hours, 

 in case of sparrows which have been flying about actively throughout the day, 

 or in bees after a day's work, show marked evidences of fatigue. These 

 evidences consist in the decrease in the size of the nucleus and the appearance 

 of vacuoles in its structure, also in the shrinking of the protoplasm of the cell, 

 which, in case of the cells of the spinal ganglia, draws away from its capsule. 

 If the cells are examined early in the morning the fatigue changes will not 

 be present, the cell having recuperated during the period of rest at night. It 

 has also been found that the Nissl granules which are present in the cell body 

 of resting cells decrease in number and show evidence of disintegration in 

 cells that have been stimulated for several hours, or that have been in pro- 

 longed functional activity. Figure 357 presents the changes in nerve cell 

 structure which can be determined from microscopical preparations after 

 various stages of functional activity. In this series worked out by Dolley on 

 the dog, i to 9 show these changes. Progressive recuperation is shown in 

 figures 10 to 13. As a matter of fact, the different individual brain cells 

 are subjected to different degrees of activity during prolonged physiological 

 strain. Hence all these cells are found in one and the same preparation, the 

 relative number varying however. 



Hodge studied the changes in spinal ganglion cells induced by artificial 

 stimulation. The results are shown pictorially in figure 358. 



The nerve processes or fibers are primarily conducting structures. But 

 fibers are susceptible to artificial stimulation, as shown in the previous 

 chapter; that is, they are irritable. They are influenced by certain changes in 

 the environment, but they do not show evidence of fatigue upon prolonged 

 functional activity. 



Nutritive Influence of the Cell Body over its Processes Wallerian 

 Degeneration. The control of the cell body over the nutrition of the 

 cell processes is demonstrated by the changes which occur when these proc- 



