PROPERTIES OF THE NERVE CELL. 



137 



tional activity the granules undergo chromatolysis, that is, they 

 are disintegrated and dissolved. Obvious histological changes which 

 imply, of course, a change in chemical structure, have been observed 

 by a number of investigators.* All seem to agree that activity of 

 the tissue, whether normal or induced by artificial stimulation, 

 may cause visible changes in the appearance of the cell and its 



Fig. 65. Spinal ganglion cells from English sparrows, to show the daily variation in 

 the appearance of the cells due to normal activity: A. Appearance of cells at the end of 

 an active day: B, appearance of cells in the morning after a night's rest. The cytoplasm 

 is filled with clear, lenticular masses, which are much more evident in the rested cells than 

 in those fatigued. (Hodge.) 



nucleus. Activity within normal limits may cause an increase in 

 the size of the cell together with a diminution in the stainable 

 (Nissl) substance, and excessive activity a diminution in size of the 

 cell and the nucleus, the formation of vacuoles in the cell body, 

 and a marked effect upon the stainable material. Hodge has 

 shown that in birds, for instance, the spinal ganglion cells of a 

 swallow killed at nightfall after a day of activity exhibit a marked 

 loss of substance as compared with similar cells from an animal 

 killed in the early morning (Fig. 65) . Dolley f also states that in 

 the dog the cerebellar cells exhibit a definite series of changes in 

 the chromatic substance, both that within the nucleus and that 

 within the cytoplasm (Nissl's granules) following upon prolonged 

 muscular activity or after such conditions as shock or anemia. 

 If these conditions are extreme, the chromatin material may be 

 entirely removed from the cells, and this he interprets as an indica- 

 tion of a functionally exhausted cell. 



* See especially Hodge, "Journal of Morphology," 7, 95, 1892, and 

 9, 1, 1894. 



t Dolley, "American Journal of Physiology," 25, 151, 1909. 



