136 



PHYSIOLOGY OF CENTRAL NERVOUS SYSTEM. 



that in functional activity acid is also produced. Mosso states 

 that in the brain increased mental activity is accompanied by a 

 rise in the temperature of the brain.* His experiments were made 

 upon individuals with an opening in the skull through which a 

 delicate thermometer could be inserted so as to lie in contact with 

 brain. So also the facts briefly mentioned in regard to the Nissl 

 granules give some corroborative evidence that the activity of 

 the nervous system is accompanied by and probably caused by 

 a chemical change within the cells, since the excessive activity of 

 the nerve cells seems to be accompanied by some change in these 

 granules, and in abnormal conditions associated with loss of func- 

 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, f 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 



^rv. <G)^ 



-4. 



5 



Jt 



Fig. 64. — 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 



* Mosso, "Die Temperatur des Gehirns," 1894. 



tSee especially Hodge, "Journal of Morphology," 7, 95, 1892, and 9, 

 1, 1894. 



